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er ica

Begun in 1895

MARCH 2007

NUMBER 371

STRATIGRAPHY AND CORRELATION FOR THE ANCIENT GULF iS

OF CALIFORNIA AND BAJA CALIFORNIA PENINSULA, MEXICO pes

Ana Luisa Carrenio and Judith Terry Smith

ANNIVERS D de

Paleontological Research Institution ee Lee
1259 Trumansburg Road Pain ae

Ithaca, New York, 14850 U.S.A.

BULLETINS OF AMERICAN PALEONTOLOGY
Established 1895

taba ee hooey tates eeeyaec ct iene cso a enteon Sasi e dy eaten nes Cena PAULA M. MIKKELSEN
DOTRECG Ree oes oO oo eS Cin gaat ae tipcgareaatay tian eter ae a Naas WARREN D. ALLMON

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nea

Begun in 1895

i
Ti

NUMBER 371 MARCH 2007

STRATIGRAPHY AND CORRELATION FOR THE ANCIENT GULF OF =
Cc

CALIFORNIA AND BAJA CALIFORNIA PENINSULA, MEXICO rm

by @

Ana Luisa Carreno and Judith Terry Smith

Paleontological Research Institution
1259 Trumansburg Road
Ithaca, New York 14850 U.S.A.

ISSN 0007-5779
ISBN 978-0-87710-467-4
Library of Congress Control Number: 2006932606
© 2007 The Paleontological Research Institution

Printed in the United States of America
Allen Press, Inc.
Lawrence, KS 66044 U.S.A.

CONTENTS

NDS CIAL Arg aneerragcarre Gabon anaes) ee uaa genleyeussONsyreagnincr x) aGWete suey ager sh sy suck cyan cy aaa ye aicsiPous iacalgsl aura ie teas eat arans) satan iteiatis eaatiern. eal wh ratedean etecen ne toa
FRESUIMEM Hy gece cates fiechrarig) oma cuepapaiscauava: an slteu‘enied ches sn fang heeswers eauphciastanr iy thc ashe beeen nie otone crmen ey Saaheue taj ane eee oNS eee oncuoe =e apee Meree ay eaten wee oe eR
MT MOGUCH ON: re ec shsrete cue tk ere yao akcoee scans ese eter a Asa omicoaed Aa yee Maetone ce Gialond pellegsyro Gye eyelets wo ooh G sales deysve deny eval obs) ae een ive
Paleogeosraphy: saya ye nas Meee bok we ty ew a eed cudpe whee Dae SRR ape a be atng, uae atari, @ Bal Gliage dgraye Tees & baeeS aubtiane
Previous <COMmelatiOmSs a grsices te airsy aes ba op syisriai ou t-suday at eas cusgsiseusl aciava sene hog eiietehe. nie emesis ei gicceeae isantertag aiteenener snare anor ass con casas usune ee
Historicalibackeround! s.c-< <.¢ seis seg SS Ge Sfeheree eg aig ©. Bim ies ud Hie deed BIRO 6 ole su cre Gep Os ae SS dle er Getereuea a o Slate oes Seo ot
Explanation:of format<and! ‘tenminolopy: ... 7d. 3% sioe.aye weve eats, Shee eo aadircay a Bowie ava anasier aye a: aiehayaec Rei siete & ayelayaes, arause @ austen
Stratigraphic terminology aires: youn tn en cispuataVat speveve tater canine sre sieienatoua a eeNeseieueun, Steuer eps cher es canine dit) aheastentanneiane snot GuSttsleneee easecee
Rock,units:. formation, member, Sroup) eis 3 2. eh bh ete Fo Sew de eae OMe ES Tote Deda ae eae eee Ge aneee ne
Mime=rock iunits? Stagesand: ZOMESy i522 5 oye cc. Sefer ays ey pote nda dl whe cae aren leie, Gerai-es ance alse /Eus tha anrdrie a lalce emer eb BLiahia igesleNSel<b pte Sale sh o.ctcceria
Informal itholo SiC UMTS yb semsy erste oye arte fe sory oh Selsitstim Boos, dad. sas ecwlseslecidt wamcee eueiho, Gereetiay te erd om ANGie e.g. Sneha, hsb ehe S eye se a Gwe ay Gta usa
MAROW ONC MOLE ae odes orcas yoyo Sut earn A Uap sey ee, ce wrested eis, feiee i pel Sus -o aris cao o GG awn rosarig Goole Mumia tay eeeanew aie re Hane eV Eioad yeaa ee coayres wine aes
ACKNOWIEUSMENTS: so oiisieee omc go ie oe tS eee ete eens, a Bat ote ay anh ie ea) Sete an Hoe ar al by olcet'd hated Uanarle ves eile wrierca)thieh gota) ai lateliaua lel al eieade 2, glands
Part I: The western Baja California peninsula: San Diego, California, to Todos Santos, Baja California Sur 2... ee
SAMUELS (EMIPAVIMENE 4 sss encisesg oMeeae oye Leis G A1e coud fo AG oraire fe pales en Ee Sy ae Sad HG po anya eee Gr) 4, Soeutyaltay ah vee, Gyo ayaa ahs wee an eh eet
Tijuanaibasin; northern Rosarito CMBbayMEMl ates. sczcaieg far sta ats GG. ctyey a ts: a gaya: fe cara! lbailedies $B RS corso atid dias) ose serstdbaey aid Ids yestentd, Suslaeyeue de seee
Ica, Misi6n basin; southern ‘Rosarito embayment... oc... swe ge esis aie sae de wud Hews Bene eRe TO Phe ee we
Rosano embayment 5/5. e.08 suces asge eo wry) Peay Rien aie: see Aaw ewe edema veut cya tala Ute Soh poe Aas, Sa aud| a whe sansa we, oR, | eas
Norther: Rosario embayment; Ensenada to ‘Punta ‘China ce scscsciscge e-cyers Ger evi stien d Guarentee) di avasacie s! ayeoe ara gogon Bode) Sed eo Seneca bacenesa
Southern Rosanovembayment as ccc edie cele ccc sited & Shae ale slolslals Goce tim sdle bat dime Gi Sigua tes Sen Bele Sele be Sg Rae Gos ele
Sani Quintin: to El Rosario; Baja: Califormia .. «24:02 405 G0 eb Saad dmetie Sean aa deat aene Sa nade ane eee eed eas

El Rosario to Mesa la Sepultura, Mesa San Carlos, and Rosarito .... 2.2... .. epee ee ee eee eee eee eee
Vizcaino EmbayMent g is...2.0 ey Sie he eid eases Uae, enw, ew NOS Eng Slee. Se Baas, Pode) eg Bek. Wile gece lghid weap Ss ROG esis Suga meee 63
IslaiCedros; northern, VizcainovembayMent,, sci sieescaie cen Grid sie, aie ceraese te eye atta, Geer ei duisl & aylennd Bs ipoenYerdeu a Bobi way im ssivenapunes woke h lpeclersuayeed
Northem Vizcaino peninsula; Punta Eugenia to Bahia Tortugas: 2.5.6 ¢.o esos a agg elev eed Seale ue dS ena ape Glauacane woe oslene d slallenalelanss) 3
Southern Vizcaino embayment, San Roque—Asuncion—San Hipolito—Punta Abreojos . 2... ee
Westermiembayment, northern part: 22.2800 50 nce tthe Ch oe dey po See a eee THE OG SEE Epo Aaa eee
ATLONOUS AUMLONACIOP aie, Sae caSecne dete jaccste, Slee nares aay ike She cralbenctete Bie cewine sits VoRETR Merete ne Sivan dest telazn Sra sheen a. mileat onus ee, eens
ATIOV OCP atrOCINIO maagitate ks ee SGeuanh, sewienarahe s ieee in a Meno ieya re Wana G Gath c) onaianaal were Teunh Oca toute Gatewe ate musdy een an ememeMe ton «he prime e arom
ATLOYOrS ani RAYIMUN On sia cea ea Se Fitia ee acwignars diay sad a aie aa, wi FER Ee Reigate! & uiad cel Mawaudls, Eoeedup Mal etvalerual a demtinteegs arse coed needs elas
Purisima-Iray basin, western slopes of the Sierra la Giganta, Western embayment .. 2... 00 2 ee
Magdalena embayment, southern part of the Western embayment .......... 0... eee ee eee ee ee ee eee eee eens
Arroyo: Salada—Santa (Rita——BU Rig es eceravie dco 5e% 6. eice ans: ove Seria d-dirw ns 0. gs isd; Bhags Sicees ois a cates fo Guahble ea, GL aleaaatig, 3 Gra eer al aleve telah eweice

EV Clem ers 2 Sus Sisce ucts Ge Susie Ghd RSS Voy [e Wieieielets ack (Gl ets, eels &, 2/8 Sebag bow ap erent ue lela eo ele aparerwle veCSee) due eu Eses si @ Rvs Biel eusndcampusmeneae es
RanchoreleA puasito dei Gastondeacih 2 dave beduatans cdg Stee had ate dig wl overeat dag Gants 0-4 i eine Mae eve G Stee Seemnlerer om mtedenD weeks
Wodosi Santos, ‘Arroyo la, Muela, southern Baja ‘California Sur’ sv ic...6 essed so Gio les cheers ands aye heehee ta tgwn a of See evaleg tale aD aneilens
Amroyorla IMME Aah «5: sim 60 elena Ve Rls SEM oie oeeal se Sw ae eee Tels quke 4G eles ae eh Sale Shea aid aE ene ap Sl geile lhe Sueueuey Samet aee
Part I: Ancient and modern Gulf of California: Salton Trough, California, to Islas Tres Marias, southern Gulf of California ........
Saltonmlrou hip wencrensy ee cnseene torah s cneher el abe venenchre terse solide eSaitndn sae ons, Botaena & sal le-arib.g"steaen ds sesirslusuin St aivenueelvis. fat aheaweks aus Gemenens! Meee ec ysmael teks
WhitewatemRiver——s aniGorgonlo Pass ane ay < mths aioMeaeni 1s aie aoe si cals tei can ey Pecks tere LE Eule Bite nap thy, Blend: bay Sie: snwas le, ereveuemein e Galea theds
Rishi@reskVallecitoj ba Sima wyeet a ssices eles sustcdurail suet eda yeea.Js ‘a ayaca seats, end Suapeug ie Bea rouaniaysberay Gli shea. Gia euaual asian ine chal neers Lo eRe ei
Southems@oy otesMoumtains: pate te esc wiek ce Sect Sap ee es sie teas vesupten ebay eh Ses es eine ned ehio Baa Weave aris eitelcovldees! nano akaaMaler of anlenene ee gee Nats
Cerro jPrictostov Sierra‘ Cucupa, Baja Calitomiay oi 36 224 gies 2.5 6 wis, Ho ee Hh DE TG SHS S Meee hotels ewe Gnelt oc a eleetee
Sani Pelipe embayment, Baja Califomial s ciccaG se eee a red sie Slee SNRs TE Tene = Oe cele Got Mee ao eave Gal awe @ eres
Slermavde; SantavRoOsaiss.c ca: sists sd alele eG Goce Gadel see weiner tM Metusl Se adhe, Gi Sinhe com eodpeble gisi-anad ghausipalabe a sGniers g Ore. ae Sudieuane cement aie
PUEKLECILOSTEIMbAY INEM ty an cus tis cas tere ce tous lenny ae) hateai ade Sere sare tah canvas acy Seenianievamaiee’ss Oe? ope. a letra nls Gites Ss eo euslane eee a torere neha ate eae Syaeenene
BahtardexGuadalupe totBaliallas Animas: (ei cede: cassia ale, a) thavare and avaiane sdiclavats, foes ress aydys cans aang eo Mores: Olea tela See renee aie
San@izorenzovArchipelace: .Sias. dive epee & he web leShs Sak Sp saw HlSuR he le mbawens feicel Diealeteue rn tang Ssivenertbr agus onlaMeleneM ere teva dati are Latieiel lave felleberrs
South westermilslam Mi burOmysS ODOLAy ssvsra totes ay tail: sees Geiss. A Sy coe wieee le Cigue ee oS A Geo hw oi adiplohokele a alehs Goes Mie) Gaeketaneneneae eesne ere
[slatSan: Esteban 3 i ssc scos Gis So Goes Gisela dad © GUBbaOn aloaitel dg ieceea seat a ES) ele Si Secee SG Rives @ tek en sent SG Wl wl ody wa ante oh Byes aves
BOlEOMDaASIM mee rtcy atcere ees ts ts, GO MENS: SME TS Re ea iI RES Se aha S, GAS ayerG.neey ore dn Siig acteh sh apernas, qieeoS Amro eg ePaL ahs, AMivin aPecaawene ets apenas aeher
[Slay SAVE OS terire, as cthay ayn SEN orca Santee ae eich reser es eteay cn ante AWA) vase Tone SaceoMib phon afew deck, fo Ep Wie a GND) decoy 04. ghae tikes loi Rll eg) CNSTS ENS RoE ENS oe
@oncepeidn Peninsula. ore bs age ge a wees beara eral theca al dd ecetlae ad Sacha ee aude e GON Ae eee cee oleae sa es eae Oa
SAMUINIGOLASHDASINE 2.006 ce ens eateetle, eke ene Nema Ne/iy dee nner lieve, es avis hinties sty euanseraw Yemties we Ghiape, ala le Vehioaale ah seeitante sansl otahane, Reon eMeeh widens: f.bhel shemstmeuaas
MOretOgemm DayIMeNt av eancyehe) ta atte che rote a ea as a eto aa tact oa AIG f6) a Nair oye dips: rf 01S: Ge) ape rely gsreNt Cos Sli. GNOM MANES Mieke Nea et RoR een eee:
KslatdeliiGarmen:s i252 80S0% Be aes DH Ewa HE See ea Da et Hea Sa Ree eee OA ee Ge Ge te eee

ES FASINTONSELT ALE cee aro teccy cess anete crcee re oa) oe ty Shae arin iBicdy Si Gl ateiaet ei car rete ah iek Be: eas laser aan wel ecisnerte Smpuecethhes Leet or sap Nays. eeeae Ua eRTuetete

ME QUCLO MASLIN Wangs ty see geese sale ty a te ete Seat eaecnns chin st GY- A rey uals Vika at VOL SUSE IPSN OR Car caian SPO ioe, Wena Pause) beaut SRR HSMM ae sae PaRNy omer Metal Mebehes
Easter Magdalenaembayment 2022.56 fisccie fb cee Gicnsh alle drei demas cae par diele s sbevaMana ci gee Glendio @alerd Oita cade a cae ean ates
San\Carlos—Punta-Sant Telmo, Tembabiche:(Timbabichi)) 2 cc-.cc0 ates egies sence ane ce ate og eee quale wile aban ahieye. a evade ole e ahaa! se

dad
81

4 BULLETIN 371

Sanmitanide Wac@ostay 2.5 @ ceeitiaeecceceustse eevesh aut au aye eset: syceiger cums estes caipslatsye) aivsigas feet auesrarie la} iclahdaya fel lafeiys ms) @eaifenan | eel sqeeeeti Ges ce, oes 93
Isla Espiritu ‘Santovand/ Isla: la Partida. ~ «6 oc. 5. csc sine seit ete ewe bce sue hao pies Sule cg we ince wuelenele Ge Sodeend ogc $n eud wre tener es auerele @ pretane) a. ctna 95
ac Paz JP emimsilar vat qevsesco arti woiego Sere atersus cine arel are ohne picunehetaahie a: ayeire ta Sieust «cuneate Calta Am fe iesiesy ose ue see os Sosy ontaneSuens
ISlasGerraly Ome cathensna suena ereptie re ee yeneten ee esnce sig aedau sic en Ausra Meyeirese wenn etever a) Gitipassgeheravenerain- anova istanet ada tarcye Met st ea recbaca raNaeencuag ore ris aye
San José deliCabo: Trowghit, ...'.. 2044.5 elotng ele « Ga eiheoe S Aas © whee hm sieiaile wt d mos maerayin eh ey eas aoe ede. BA wendy oes ote eel Gaterae ane
Arroyo la Trinidad, Rancho El Refugio
Rancho -Alsodones, ‘SantasAmita 2 i ..6.5 stenececsngleveceed ay cyeela tl a celve 3.50 Faye a atop rey wuld aire cat tna, aia ho Beaute Gehan a Ca es alow tas Mela Goo ase Gea at
Islas tlmesuNviariassiINay anit esc cence oeaetrmiccnees wncacee 2 oy Gieue hey eeeteneta ecu anses cuteness es wireheusteneutienielte dimey sree eRerens pe ceaaneue es ecgren winces
Punta Mitta Nayarit’. oc Gee cee ase foie a some dae ak fee ge tee cares Gonna bee whee Soe Gre Goa eae ele 2 dal eG Che, Ge eve Sign th et ee
Conclusions... ....:+. +: 5B Sevainar Bi vesedonttuks dia OE pl Gnbienas gi Bld se bP hele ty ang Bez Sl mvietan Huenerip tan Hate dieu’ ay abo dvs wy dhatren Gr Se chbaen basi ci ae cup aunt aes
Referencesserted! x2rcec, ae eee crcve suseeas ait euphoria ons poccumi Susy ehaeSum oder (ec aite. ue) S00) GOW a Pons ey eal cereale ons eibseed runs: aitvine, cueyeeerone ne to mteas, Sonate
Appendix I: Selected paleontological and radiometric references, by embayment ..... 2.2... 02 eee
Appendix II: Cited topographic quadrangle maps, southern California, Baja California, and Baja California Sur
IMGEX: c-kit fa nes be eet 28 ta) Rag en eae RE ona ctienTee anes ey eeeTN SD cats evosg ra ue aigsapel eee saey Saenger oes Kerth aera ae

LIST OF ILLUSTRATIONS

Text-figure Page
1. Ancient and modern Gulf of California and the Baja California peninsula, index map showing the principal geographic locations
Gifed: inethisspapetie Ole t-: 4 2) marcecusyautentensores Roeheasi mn a cuars, 87s Shegee erage rather epee er Recast as Gill 4 recht «esteem ott neem weet ees 9
2. Embayments, map showing southern California, U.S. A. to Cabo San Lucas, Baja California Sur, Mexico 10
3. Quadrangles of the San Diego embayment and northern Rosarito embayment (= northern Tijuana basin). 15
4. Rosarito embayment, Tijuana basin in the north and La Mision basin in the south... . 00... 0. ee 18
5: (Rosario‘embayment, northém" part), Ensenada.to' El Rosamo; BiG.) 4.2%. 4.5522 26.082 0s Stats cas ag oe etn ee tee eee 23
6. Southern Rosario embayment, map showing El Rosario to 28° N, including Mesa la Sepultura, Mesa San Carlos, Punta Maria, and
Lomas las, Tetas:de‘Cabra: © 2-2. s.as @ 2's cm Big St «nw 2 whoo aah SUR cee GS lens heels wk ene eb mve ng tusuthe @hontus im bbhor eaten ohenane Guaheduahenen ers 24
7. Isla Cedros, B.C.S., map showing Neogene marine outcrops and general geology modified from Kilmer (1984). 2... .....0....-. 28
8. Arroyo Choyal, northeastern Isla Cedros, area of California Academy of Sciences locality 946 collected by Hanna and Jordan in
OS Perk uk Rec eens neh aies Ses Mega a cay 0, Clk eam RMR RN ONS Rev ERS Been PET oR: Pgs Oy, 5 05° Se ee Ree fee eee et 30
9. Arroyo Choyal, outcrop in small canyon to the south with unsorted conglomerates containing disarticulated valves of the Late Miocene
pectinidivropecten.sallegost(Mordam and Hertleim).: ajc sc iecice g¥e anes 6 anetsk eis vanieriecg?s cus 4 Gh aleue ot sh agamens usasihs anes! auasfaveNeMa lve te: stedens 30
10. Vizeaino‘embayment, map:of Isla‘Cedros to Laguna’San Isnacio; BiC.S.. acs nase s eva eee hea eee ees Os eee Seek 30
11. Martin Lagoe standing on the angular unconformity between brown turbidite sands of the Cretaceous Valle Formation and light-
colored pelletal phosphorite and sand facies of the Miocene Tortugas Formation. ... 2.2... ...0..-.-0.-0-.0-50-50-05--00-50-- 30
12. Monadnock of highly fossiliferous Late Miocene Almejas Formation sandstones, 3 km southeast of Bahia Tortugas. ... 2.2.0... 30
13. Western embayment, San Ignacio to Arroyo Mezquital, with outcrops of the Eocene marine Bateque Formation. .............. 37
14. Arroyo San Ignacio, view from Rancho el Estribo at type area of the Late Miocene San Ignacio Formation, 4—8 km downstream
FLOM SAM LOMACION 0.12, pe-nixcnes ned ate uate te fecal re ed eel antes eaten ated NSE MA eure nC 2 2 TSM RS Np orate name ew ce es veN Sse es aaralke ee ca rene 37
15. San Ignacio Formation, south wall of Arroyo San Ignacio showing fossiliferous marine sediments overlain by an unnamed volcani-
clastic sandstone (possibly the Atajo Formation of Mina-Uhink, 1957) and capped by the Late Miocene basalt of Rancho Esperanza.
EA ieee ee ae ee RS fe ea seen eset ee acer eae tae et en ee aes aT SCONE Preece OR EE IEE e IC De oR ec eee Ga 31
Lore Mesavel Yesosnorthsside: Of Arrovoy PAWOCiM1O® eisiancrcusr ets ebsites alteuievistten sat tarts ivel/<tts falc igi 20a rtet eifayrauter's am) hyentelis atyelestini @ aveveaay ae qpuatretanled yor 37
17. Arroyo Mezquital section of Eocene Bateque Formation siltstones overlain uncontormably by the Miocene Isidro Formation. .... 37
18. Western embayment, south of Arroyo Patrocinio to San José de Comondu, map showing southernmost outcrops of Eocene diatomite
Inuwesternm North: AmirermiCa. He ..2, acc siete, ke ene ears erreacees tee tine unte east erate tea etre satanrelaa pf enect ou ea cle c w unsere oes erate erent w acres ices pet ay ce ere Geereye 40
19. Bateque Formation, Eocene foraminiferal facies in Arroyo Mezquital. .. 2... ec ec eee et eee eee re bee eae 40
20. Contact between the Miocene Isidro Formation and underlying Eocene Bateque Formation marked by bulbous burrows, Arroyo
I (e405 E21 cia eet Cr ae ae ee el Ceaser Re aet one art er Pee iron caren s Gebers recieaecpn eat woep raya tere mee nLce coy Aten eno es uec menor ert 40
21. Phosphatic and diatomaceous beds of the Oligocene San Gregorio Formation exposed in Arroyo la Purisima near the dam (/a presa)
AU Sams [SIAKOR? sedate so sirius Ga po. 'eve,ig ce promaate seu re eaten sy) OMe Bi ctae yal aster ake iro) ore euiey ens everett Gy saee eel suse alien age eusehe ha ant hie meme neteate 40
22. E): Pilon, view northwest across. Arroyoula Purisima, from: San Isidro.” 252262 ae c= a eae CAG ee eee See Oe 40
23. San José de Comondi, type area of Middle Miocene Comondti Formation. ...... 0.2... e ee ee ee ee eee 40
24. Arroyo La Salada and the Magdalena Plain, view southwest at Heim’s type section (A—B) and mezquite trees that mark the site of
Rancho La Salada. onthe Pleistocene itemace: aaa stg asn geste ee Saree Sem ee eee @ eevee sg rnGis ure cut he eterna cee eee 48
25. Salada Formation at B, southwestern end of type section. 48
26. Tobias Schwennicke surveys scattered bricks that remain from Rancho La Salada. 48

27. Fossiliferous clast of well-indurated gray sandstone in Arroyo La Salada, upstream from the site of an old fort. .............- 48
28. Salada Formation, map of type area south of Santa Rita and El Médano. ... 0... 1. ee ee eee 48

68.

69.
70.
Vilie

U2
13:
74.
AD.
76.
Tiles

78.

. Southwestern Isla Tiburon, Sonora, locality map modified from Smith (1991c).
~ Miocene volcanic breccia, southwestern Isla Tibur6n. 5....6.5:605 6 seen she Baie He ee ene whe eee eH Cae eee

. Loreto onshore embayment, sketch map of major arroyos, modified from McLean (1989).
. Arroyo de Arce, prominent cliff with cavernous weathering in calcareous sandstone and coquina of the east-dipping Carmen-Marquer

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

. Giant pectinid molds from the contact between Heim’s beds 2 and 3 at the old fort section, . 2... 02 ee

Magdalena Plain, map showing old ranchos and other landmarks. . 2... 0 0 ee

. Cerro Colorado (highest ridge) and Cerro Tierra Blanca (below and to the right), type sections of the El Cien Formation, Cerro Tew

Blanca:and':Cérro; Colorado: Members. 22: s.2 cess ae aise Sed ts Decca ciawags od ate Bladavepieng teva dette gs emis Goble aris @erehepeyarg Gate ne dun «
Arroyo San Hilario, type area of the San Hilario Member, El] Cien Formation. ........0.0.00.000.00 20000000000 00005.

El Cien Formation, map showing type sections and study areas from Applegate (1986) and Fischer ef al. (1995). 2.0.0.0
Silicified wood, float specimens from the El Cien Formation, Cerro Colorado Member, near La Fortuna. ...............0....
Paleogeography of the Baja California Peninsula and ancient Gulf of California, map based on distributions of Late Oligocene to
Holocene marine mollusks and associated microfossil and radiometric data... 2. 2 ee

. Arroyo la Muela, north of Todos Santos, B.C.S., where the weathered Salada Formation forms pink, green, and brown badlands

LOPOSTAPH Ys) 52,0 4 .asynne Se tenn aor Se Rae HDs we else Gacpien ge ath aR Wears a arm ac yada days ai@ Ruaen dep clos ane gual ea ake Sa the aires

. Salada Formation, coquina and sandstone facies in one-meter-high bench at the base of la Loma el Bayo Flojo. ..............

Salton Trough, map of the ancient Gulf of California, northern part from San Gorgonio Pass to San Felipe, B.C. 2... .........
Imperial Formation in unnamed, south-flowing tributary to Super Creek, east of the Whitewater River, northernmost Salton Trough.

- Split Mountain Gorge, Miocene reddish-brown alluvial fan deposits exposed in Fish Creek Wash. .. 2... 20002000002 ee ee
- Canon Rojo area, western Sierra Cucupa, where scarps of the northwest-striking Laguna Salada Fault and the northeast-striking Canon

Rojo Fault meet to form a corner of a pull-apart basin (Mueller and Rockwell, 1991). 2.20... ee
Unnamed granitic beach deposits northwest of San Felipe contain internal molds of Pliocene mollusks. ....................
Puertecitos embayment, map showing Neogene marine type sections. ..... 2... 0... 0c eee eee eee
Puertecitos Formation, view from south of Arroyo El Canelo toward Mesa el Tabano (dark rocks in left background). .........

. Matomr Mudstone Member, west of the road from San Felipe to Puertecitos. 2... 002 ee

Bahia de Guadalupe to El Barril, map including Isla Angel de la Guarda.

Tres Virgenes to Santa Rosalia, B.C.S., index map to the Boleo basin and surrounding area. ... 2.2.2... ...00.0.00.0.00.05005.
Boleo basin, ridge between the headwaters of Canada Gloria (drainage in the background) and Arroyo del Boleo. ............
Tirabuzon Formation, type section along Mexico | north of Santa Rosalia. 22... 200.0000. 0 ee
Loma del Tirabuz6n, northwestern end of the type section of the Tirabuzo6n Formation, which dips to the southeast. ...........
Gyrolithes fragment with surface ridges interpreted as scratch marks made by the organism that dug the burrow (E, C. Wilson, 1985).
Gyrolithes, the corkscrew part of a burrow, with an “associated Thalassinoides ‘turnaround’ ” at the lower end (E. C. Wilson, 1985).
Boleo basin arroyos mapped by I. F Wilson (1948) and I. EF Wilson and V. S. Rocha (1955), including the type section of the Tirabuzon
Bonmatoneoig CarrenOn (lO SIN) ease cect cecsna dante te, auethane hartinehar deity eine we depSasarre ace, stad Soe heuer ae deer Ohea daca ret ak Sau Shera a Sheree) Mode hey Mime ane cee

Gulf islands and index map of important localities in southern Baja California Sur... 0 ee

La Giganta (right, 5,794 m) and the Sierra la Giganta crest, view west from Arroyo el Le6n, Loreto embayment. ............-
59. Amusium toulae (Brown and Pilsbry), U.S. National Museum hypotype no. 418203, from Punta Pared6én Amarillo. ........
Goncepcion Peninsulaslocation) Map. 2% cece Gs en eKe a aed eeG cg dees eecnee se ee HOSES Geeta Ose Ewoees Sees ee

. Punta Paredon Amarillo and the unnamed Miocene yellow conglomeratic sandstones west of Punta Concepcion. .............
. Isla‘€armen, map of the eastern or offshore Loreto embayment. .....6..3..220 55003 oko ee cee ee ee ee ea bea eee

Formation, ‘undifferentiated (locality 2 of McLean, 1989). 3.2.03 6 cece ee eee ee ee ee eae dee ae we hele

. Loreto embayment, view west from Mexico | at km 12 of the Carmen-Marquer Formation, undifferentiated, and interbedded Late

Pliocenestuitsu(NicIweamy OBO). e siaraca ee a: faran ga raters aevmvce ane! seraviale sce: ba. -aleeeac angi bsE ane aaecenapamaren eigen saatavavelauseaiers alolen a ERnaet ee

. Arc-volcanic and voleaniclastic rocks, Oligo-Miocene vent and near-vent facies north of Loreto and south of San Bruno. .......
. Unnamed Oligocene (’?) red cross-bedded aeolian sandstone in Arroyo El Salto, 500 m downstream from Rancho el Salto (locality

U2 TOLIMCIcan ORO) eee: see cas seve ste ate apeae go ocecapeiciaaeiee Sue GuGle Me mea Grcike GEE sewed Shacoans AA agus Se art cea ee Oe nD See
Cornwallius bed in the El Cien Formation exposed at low tide, northern side of Arroyo San Carlos, eastern edge of the Late Oligocene—
Barly Mioceneeaster Masdalenajembayment... 2.25 eqn eae nu eek aid de ta me Law OR AEE Ow Eee E A CoAT eae nee as

Punta San Telmo, Tembabiche, and Punta Montalva, map of the eastern Magdalena embayment.
Red cross-bedded sandstone referred to the early Late Oligocene Salto Formation, south of Arroyo Montalva. ...............
Los Pargos formation, Late Jurassic—earliest Cretaceous unit exposed at the core of an anticline 1.5 km northeast of Arroyo Tem-
babiche(Plata-Hemandez +2002). ess ic ecduser @ananshepaom aiepe Wt AS Gos 8 ew EF RIG oP angia sh Haat Ro Aga hes autee gy Sle 48 0 Gabe
La Paz tuff, northern side of Arroyo el Sauzoso, south of San Juan de la Costa and Punta Los Tules. 2.2... .-....-0..-......
San Juan de la Costa and the La Paz peninsula to Cabo San Lucas, index map of key localities... 2.2... 00.00... ee
San José del Cabo Trough, map showing important features, ranchos, and type sections... 2.2... 0.02 ee
Isla ‘Cerralvo,. “Farallones blancos,” near the site of Ruffo’s rancho. 2.5.2.2. cn eee eee ee eee tee eee de ne ee we gees
Junction of Tropic of Cancer (approximately 23°25’ N) and Mexico |, view west at the Sierra la Laguna. ..................
Coarse-grained conglomerates with fragments of oysters, the gastropods Oliva, Melongena, and Cancellaria (Pyruclia), west of
Mexicomllatithe: Tropic:of Cancerjmarker “2. coh a Shea ae Bd eG aa ea Baye ede ad ee we ee GA a Sees
Refugio Formation, type section at Rancho el Refugio with poorly preserved Early Pliocene fossils, including the abundant pectinid
Puvola refugioensis, (Hertlein)) [=-E. keepu(Atnold)). . ac sac co SG swede, hs oa eye ds G a RNS ws Oe Shea Heyes. s aed

90
90

6 BULLETIN 371
79, La Calera Formation, red cross-bedded sandstones at the entrance to a box canyon in the type area near junction of Canada la Calera
Width A Troy ael Misi LAGS pcre ue ecleses onc cavers pastente ya oo Aamcnc dey oer cn Maratea al et tee eectg sm eucan ites acute letra Metfatiel Selecta sui ePisusjeatiaettones1 sesiest len syreuran cas eens 102
80. Trinidad Formation, basal Member A, type locality in Arroyo la Trinidad... 2. ee 102
81. Isla Maria Madre, index map and geology modified from Carreno (1985) and McCloy et al. (1988). 2... 6 eee 103
LIST OF TABLES
Table Page
js, San Diego: embayment, Jithostratigraphic Units:, ¢ sc & caves seeps ts eo aeiavs, Viodele a “pea iene. eetiela pss Sos elie alle at ah 4,6 ates Gp here esc eh aee 16
2. Rosarito embayment, Tijuana and La Mision basins, lithostratigraphic units. 2... 0. eee 20
35) Rosario embayment; lithostratisraphic Units. 5 i.e 7 gcyh aa Ge ave Syne xs Sgn eG dove Dope Sywens 2 aban Siena A Bee ote wt hayes ae 26
4. Vizcaino embayment, Baja California Sur, lithostratigraphic units. 2... ee 32,
5. Western Magdalena embayment, lithostratigraphic units. 2... 0... ee ee ee eee eee eee 45
6. Salton Trough, California and Baja California, lithostratigraphic units. ©... 0... ee ee eee 62
7; Goncepelon Peninsula: IthostratieTaphic UMitS.. yaar da tyaverd e-gitm whales dquesth af dr sasnarene @\qraya ee ane vives dagee, anetarae scarab ahaud es8 euene, Be eaape ee 82
8, San José:del ‘Cabo: Trough, lithostratigraphic units; 22.0% <ac8s ee ea cele See cls Re eS tae es be ee ea Ses os emt woes 99

BAJA CALIFORNIA STRATIGRAPHY; CARRENO AND SMITH ih

STRATIGRAPHY AND CORRELATION FOR THE ANCIENT GULF OF CALIFORNIA AND
BAJA CALIFORNIA PENINSULA, MEXICO

ANA LUISA CARRENO

Instituto de Geologia, Universidad Nacional Aut6noma de México, Circuito Exterior, C.U.,
Delegacion de Coyoacan, 04510 D.F, México
anacar @ servidor.unam.mx

JUDITH TERRY SMITH

2330 14th Street North, #401, Arlington, VA 22201-5867, U.S.A.
Redcloud 1 @earthlink.net

ABSTRACT

This paper presents the first comprehensive stratigraphic correlation charts for both the Baja California peninsula and the Gulf
of California area since Durham and Allison (1960). Forty-five columns show stratigraphic or lithologic units for San Diego,
California through western Baja California, Mexico, and the Salton Trough of California to the Islas Tres Marias, Nayarit, Mexico.
Correlations are based on published and unpublished stratigraphic, paleontologic and radiometric data. The columns refine the
chronostratigraphic context for interpreting the geologic history of the ancient Gulf of California and a series of embayments
along the western Baja California peninsula. We summarize upper Mesozoic to Quaternary stratigraphy, but emphasize Tertiary
marine units, including those that were described formally in accordance with the North American Stratigraphic Code (1983),
informal units that were introduced without full locality and stratigraphic data, and unnamed lithologic units that need further
study. The lack of detailed geologic mapping over large parts of the area accounts for much of the variation in formal stratigraphic
nomenclature. Periodic reviews are needed to improve age data and constrain events in this structurally complex area, which
includes the Basin and Range Province, the San Andreas Fault system, the East Pacific Rise, the Gulf Extensional Province, the
Puertecitos Volcanic Province, and the California Continental Borderland. Selected references to paleontologic and radiometric
data are listed in Appendix |. They document the earliest seawater in the northern Gulf of California in late Middle or early
Late Miocene time, multiple marine incursions into the Salton Trough of California, and more refined chronostratigraphic ranges
for such problematic units as the Imperial Formation, Comondu Formation, Salada Formation and El Cien Formation.

RESUMEN

Se presenta la correlacion y la discusi6n de 45 columnas que representan las unidades litoestratigraficas que han sido empleadas
formal o informalmente en el area comprendida entre San Diego, California, EUA a través de la costa occidental de la Peninsula
de Baja California, México (Lamina I), y el Salton Trough, California, EUA hasta las islas Tres Marias, Nayarit, México (Lamina
II). Estas columnas estan basadas en informacion estratigrafica, paleontologica y radiométrica publicada e inédita y constituyen,
después de la publicacion de Durham y Allison (1960), una significativa contribucién en el contexto cronoestratigrafico para
interpretar la geologia historica del antiguo Golfo de California. Se resume la estratigrafia desde el Mesozoico superior hasta el
Cuaternario, con énfasis en las unidades marino-terciarias, incluyendo aquéllas que no fueron descritas formalmente de acuerdo
con el Codigo de Estratigrafico Norteamericano (1983), es decir, unidades informales que han sido introducidas sin una adecuada
y completa descripcion, asi como unidades que necesitan ser redefinidas o reestudiadas. La falta de levantamiento geolégico
detallado en la mayor parte de la region ha fomentado el incremento de la nomenclatura estratigrafica. Sera necesario realizar
revisiones periddicas con la intenci6n de calibrar la edad y los eventos ocurridos en esta area tectonicamente compleja, que
incluye la Provincia de Cuencas y Valles, el sistema de fallas de la Falla de San Andrés, la Cuenca pacifica del Este, la Provincia
Extensional del Golfo, la Provincia Volcanica de Puertecitos y el Borde Continental de California. Se ha incluido importates
referencias con informacion paleontologica y radiométrica, documentandose asi la presencia de agua marina en la regién septen-
trional del Golfo de California, durante el Mioceno medio tardio o el Mioceno tardio, asi como multiples incursiones marinas
en el area del Salton Trough, California. De igual manera, esta informacion proporciona alcances cronoestratigraficos mas con-
fiables para algunas unidades problematicas como las formaciones Imperial, Comondu, Salada y El Cien.

INTRODUCTION Baja California and the adjacent islands in the decades

from 1970 to the present. The region is an exceedingly

Heightened interest in the geology and tectonic his- complex plate boundary area, and invites models and
tory of the ancient Gulf of California brought more topical studies in many disciplines. These require a

than 150 scientists from more than ten countries to time-stratigraphic framework, early versions of which

8 BULLETIN 371

were established for local basins over the past 80 years
without regard to the overall history of the ancient
Gulf and peninsula. Beal (1948), Anderson (1950),
Mina-Uhink (1957), Durham and Allison (1960), Lo-
pez-Ramos (1973), and Gastil et al. (1975) published
the most comprehensive correlation summaries of the
area’s geology. Because any time-stratigraphic context
needs periodic review to incorporate new mapping and
dating, we update earlier charts by modifying or con-
structing 45 reference columns based on our best in-
terpretation of available paleontologic, stratigraphic
and radiometric data.

Tertiary stratigraphy and biostratigraphy is our em-
phasis, but we include references to older units and
cite studies of Quaternary deposits where available.
Batholithic and pre-batholithic units were summarized
by Walawender er a/. (1991) and papers edited by Gas-
tl and Miller (1993). Comments on Cretaceous marine
units were provided by LouElla Saul (written com-
munication, 2003).

Pleistocene data are presented in an exhaustive re-
view of terraces along 3,000 kilometers of coastline in
the gulf and Baja California peninsula; Ortlieb (1991)
related terrace profiles and ages to rates of vertical
motion and sea level fluctuations. A review paper by
A. G. Smith ef al. (1990) included mostly Holocene
but some fossil records for the land mollusks of the
Baja California peninsula, many of which are repre-

sented in the collections of the California Academy of

Sciences, San Francisco, California. Taylor (1983,
1985) discussed Holocene freshwater mollusks of the
lower Colorado River and eastern Salton Trough and
related species to drainage patterns.

This paper summarizes current knowledge of the
age and extent of important lithostratigraphic units,
synthesizing data from published and unpublished
sources to refine ages and to improve correlations be-
tween marine embayments and structural provinces.
Ages are based primarily on paleontological data for
Tertiary marine sediments constrained by Tertiary to
Quaternary radiometric ages for associated volcanic
units.

The geographic extent of this report is shown in
Text-figure 1, from San Diego and the northern Salton
Trough of California to southern Baja California Sur
and the mouth of the Gulf of California. The text is
organized in two sections that describe the columns
from San Diego and the western Baja California pen-
insula (Part 1) and those from the Salton Trough, Cal-
ifornia to the Tres Martas Islands (Part 2). The em-
bayments represented by columns are indicated in
Text-figure 2. The peninsula is divided into two states
at 28° N: Baja California and Baja California Sur. The
last published reconnaissance geologic map for the

northern state was by Gastil er al. (1975). Beal (1948)
and Mina-Uhink (1957) provided the most recent pub-
lished geological maps for the entire southern state.

Paleogeography

An extensive body of literature documents a time
When the Baja California peninsula was attached to
mainland Mexico, prior to the onset of spreading and
crustal thinning approximately four million years ago
(Dauphin and Simoneit, 1991). A volcanic are occu-
pied the area of the ancient Gulf of California from
24 Ma to 12 Ma (Hausback, 1984a,b; Sawlan, 1991).
The first seawater invaded the ancient gulf as early as
12.9 million years ago (Gastil ef a/., 1999; J. T. Smith,
1991b), before the Pacific/North American Plate
boundary shifted from west of the peninsula to inside
the present Gulf. The area includes or is near the Basin
and Range Province, the San Andreas Fault system, a
segment of the East Pacific Rise, and the Gulf Exten-
sional Province. Discrete Neogene basins that devel-
oped in the western Gulf of California differ from each
other in structural setting and chronostratigraphy; all
exhibit a great variety of facies.

The western Baja California peninsula is part of the
California Continental Borderland. In contrast to the
Gulf side, the area was covered by extensive Creta-
ceous to Tertiary seas that at times extended as far east
as the edge of the present Gulf of California (Text-fig.
35, p. 54). Except for the Vizcaino peninsula, the
southwest coast of Baja California was structurally ho-
mogeneous during Tertiary time: sediments were
slightly warped or tilted, uplifted, then capped north
of the Magdalena Plain by extensive lava flows that
emanated from the central part of the peninsula.

Helenes and Carreno (1999) related the Neogene
sedimentary history of Baja California to the 22 struc-
tural domains defined by Fenby and Gastil (1991).
Those subprovinces included an eastern protogulf from
13. Ma to 5 Ma and a modern system of pull-apart
basins that began at approximately 5 Ma (Fenby and
Gastil, 1991). Henry and Aranda-Gomez (2000) re-
garded the Middle to Late Miocene (12—6 Ma) east-
northeastern extension in the Gulf, which formed the
Gulf Extensional Province, as part of a broader south-
ern Basin and Range extension.

Previous Correlations

Comparative stratigraphic columns for all of Baja
California are included in the reports by Beal (1948),
Anderson (1950), Durham (1950), Durham and Alli-
son (1960), and J. T. Smith (1991c). Regional corre-
lations were given by Helenes and Carreno (1999),
McDougall et al. (1999) and McLean ef al. (1985,
1987), among others. Gastil et al. (1975) focused on

BAJA CALIFORNIA STRATIGRAPHY

: CARRENO AND SMITH 9

120°.W CALIFORNIA ~\. _ ( now | 105° W 100° W
x I\. fo oe |
, Northern Channel Islands *\ rivet |
\ 0 Ri\
Transverse v | 35° N
35° N ( Ranges = | 7
x < ARIZONA NEW MEXICO
x oT S |
\ Los Angeles L
‘ 0 | N
ro’) ae
Ze San D Tucson |
We. é !
\% | UNITED STATES 0 250 KM
\e —--—/-
%
\2x.
30° N \ Q 30°N
S y
ore
@ ?
o %.,
—_ Vizcaino ee
a Peninsula 4 0.
Tos “ce
oO sie oe
Sierra la ©
\Giganta , i 26°N
26°N : 7
a \ 4 u a
Cc \ . ie
Magdalena Plai
Ss cand "Todos Mazatlan \_
oC Santos Cabo = \ -
2 ; ‘ Trough Cee ice
Sierra la Laguna- > L If ¢
an! gta tp. oy, < r
Sierra laVictoria oo ar om at 2
0% Ss 2 Ls f
oF “> > ( im fs
S
Punta Mita-<¢ 7 a
aon Puerto Vallarta jarisco om FN ~ 20° N
Z \ ps
~ wy; pV
f or? Lon,
COLIMA A irene 4
BA
La Mira Basin ¢ GUERRERO
AM, Arroyo Matomt IM, — Isla Monserrate Pu, Puertecitos Acapulco
AS, — Arroyo la Salada gy Isla Tiburon SC, Sierra Cucapa
B.C., State of Baja California L; Loreto SF, San Felipe
BCS, State of Baja California Sur LM, La Mision SGP, San Gorgonio Pass,
CM, Coyote Mountains ILP, La Purisima Whitewater River area
CP, Concepcion Peninsula Mx, = Mexicali SL, San Ignacio
CPr Cerro Prieto PL, — Puerto Libertad SR, — Santa Rosalia
Cu, — Culican PP. Puerto Penasco ST, Salton Trough
IA-G, Isla Angel de la Guarda PSA, Punta Santa Antonita, TB, — Turtle Bay, Bahia Tortugas
ICa, Isla Carmen Punta Pulpito 3M, Islas Tres Martas
ICe, Isla Cerralvo PST, Punta San Telmo

Text-figure 1—Ancient and modern Gulf of California and the Baja California peninsula, index map showing the principal geographic
locations cited in this paper. Map modified from J. T. Smith (1991c).

10 BULLETIN 371

CALIF.

ag Angeles C 113° W 11

1 Us san Diego

ARIZONA

EI Rosaric
30°N
L
\N ya\ °
Ne 140) \

‘ \
Guerre — \ e(iuaymas

Negro \ S68, Santa a

a) x a oris
ioe

Hermosillo

Cabo San José
Q
: ‘ , . 2] Cabo
115° 00'N San Lucas “*
Text-figure 2.—Embayments, map showing southern California,

U.S.A. to Cabo San Lucas, Baja California Sur, Mexico. North to
south, Plate 1: 1, Los Angeles basin; 2, San Diego embayment (En-
cinitas, California, to La Joya, B.C.), overlaps 3, Rosarito embay-
ment, including Tijuana and La Mision basins; 4, Rosario embay-
ment; 5, Vizcaino embayment: 6, Western embayment, which in-
cludes Arroyo San Ignacio to Arroyo San Raymundo and 7, Purt-
sima-Iray basin, and 8, Magdalena embayment; 9, Todos Santos
North to south, Plate 2: 10, Salton Trough; 11, San Felipe embay-
ment; 12, Puertecitos embayment; 13, Isla Angel de la Guarda em-
bayment; 14, southwestern Isla Tiburon; 15, Boleo basin; 16, Con-
cepcion-San Nicolas embayment; 17, Loreto embayment; 18, Arroyo
San Carlos to San Juan de la Costa, the easternmost Magdalena
embayment; 19, Cabo Trough. Tobias Schwennicke (oral commu-
nication, 2003) suggested that southern Magdalena and Todos Santos
embayments might once have been connected.

units and correlations for the Santa Ana Mountains,
California, through the northern state of Baja Califor-
nia.

Darton (1921), Heim (1922), Beal (1948) and Mina-
Uhink (1957) introduced a number of formation names
that were subjected to much reinterpretation and in
some instances misuse, leading to long periods of

faulty correlations of units of different lithology, prov-
enance and age. Because of the international interest
in the area and the difficulty in obtaining some reports,
this paper provides a chronostratigraphic context as a
starting place for further refinement of basic data. Our

comments on such problematical formation names as
Imperial, Comondu, Salada and El Cien are given in
the text for the embayments that include their type
sections.

Historical Background

In California, William P. Blake made the earliest
sketch map and geological observations of the Salton
Trough and the Peninsular Ranges during explorations
for the Pacific Railroad (Blake, 1857, fide Testa, 1996;
1858). Kew (1914), Mendenhall (1910), and Brown
(1923) published early papers that included maps with
fossil-collecting areas and some geology. More recent
geologic maps are cited in the text that describes each
column. The most important papers for early strati-
graphic nomenclature in the ancient northern gulf are
Vaughan (1917), Hanna (1926), Woodring (1931,
1932), Allen (1957), and Dibblee (1954, updated in
1996a). Dall (1874, 1898) and Arnold (1903) estab-
lished the San Diego Formation, the first formal lith-
ologic name in the San Diego area.

South of the border, the first traverse of the entire
peninsula was made in 1867 by W. M. Gabb, on loan
from J. D. Whitney and the California Geological Sur-
vey to lead one of the field parties for the J. Ross
Browne Expedition. Financed by the New York and
Lower California Colonization Company, the explor-
ers went by boat to Cabo San Lucas and zigzagged
north along old trails used by the indigenous people
and the padres. Later known as a pioneer of California
paleontology (Gabb, 1869b), he collected only a hand-
ful of paleobotanical fossils during the expedition and
did not name any stratigraphic units. His official geo-
logic report was written in June 1867 but published in
a Supplementary Appendix to J. R. Browne’s ‘‘Re-
sources of the Pacific slope’ (Gabb, 1869a).

Other early references to Baja California geology
are contained in the papers of Lindgren (1888, 1889,
1890), Emmons and Merrill (1894), Willis and Stése
(1912), Darton (1921), and Bése and Wittich (1913).
Nelson (1921) provided a good overview of the ear-
liest surveys, natural history, roads, trails and ranchos
in his report on the biological survey of 1905-1906.
Access for these early Baja California expeditions was
by boat and by pack animals; the Transpeninsular
Highway (Mexico 1) from Tijuana to La Paz was not
completely paved until December 1973.

Formational names for the principal Cenozoic sed-
imentary sequences of the Baja California peninsula
were first proposed in the reports of the following:
Darton (1921) for the Sinclair Exploration Company;
Heim (1922) for a Swiss Colonization Company; Beal
(1948) for the Marland Oil Company; I. F Wilson
(1948), and I. FR Wilson and Rocha (1955) for the Insti-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 11

tuto Geolégico de Mexico, the U.S. Geological Sur-
vey, and the Comité Directivo para la Investigacion de
los Recursos Minerales en Mexico; Anderson (1950)
and Durham (1950) in the volume on the 1940 E.W.
Scripps cruise to the Gulf of California; and Mina-
Uhink (1957) for Petréleos Mexicanos (PEMEX). Oth-
er new formational names and members, some formal
and some informal, were introduced by Santillan and
Barrera (1930), Flynn (1970), Kilmer (1963), Carreno
(1981, 1982), Minch et al. (1984), Ashby (1989b),
Martinez-Gutiérrez and Sethi (1997), Martin-Barajas
et al. (1997), and Ledesma-Vazquez ef al. (1999,
2004).

Explanation of Format and Terminology

Representative stratigraphic columns are shown
north to south for San Diego, California to south-
western Baja California Sur (Plate 1) and tor the Sal-
ton Trough to the Islas Tres Martas, Nayarit (Plate 2).
Units are plotted on the time scale of Haq ef al. (1988).
Data, in some cases summarized in tables, include au-
thor, original reference, status of formation name (for-
mal or informal), type locality if designated, general
lithologic description, geographic extent and age:
where available, thickness and contacts with adjacent
units are also given. Nomenclature reflects ongoing
studies as well as published and unpublished reports.
Subsequent papers by cited authors should be antici-
pated and consulted. See Appendix I for selected ref-
erences to papers on paleontology and radiometric
ages, and Appendix 2 for a list of quadrangle maps
cited herein.

We have grouped the columns by embayment for
convenience, realizing there is overlap in some cases:
many embayments were at times more extensive and
perhaps interconnected. Generally, we use “‘embay-
ment” for the most extensive features, “trough” for
narrower areas commonly delineated by faults, and
‘“basin”’ for less extensive areas of marine outcrops.

Formally named stratigraphic units are those de-
scribed in recognized, widely available scientific pub-
lications according to the rules of the North American
Stratigraphic Code (1983), the most recent guideline
for classifying, defining and naming of geologic units.
Names that were proposed in theses, mentioned in ab-
stracts or unpublished reports, or that were incomplete-
ly described, are included in our columns if they have
come into common usage through field trip guide-
books or other regional references. We regard these as
informal names of the author in question; their inclu-
sion here does not validate them as formal names.
Problems of stratigraphic nomenclature are discussed
under the columns containing the type areas of for-
mations. Our cited paleontological references include

principal sources of data but are not intended to be
exhaustive.

The formal classification of a formation promotes
understanding based on a clear concept of the rock
unit, unambiguous communication between scientists,
and nomenclatural stability, especially when the unit
is correlated beyond its type area or across an inter-
national boundary (the Imperial and Otay Formations,
for example). Observing the rules of priority conserves
well-established names and avoids the confusion of
multiple formations with the same name, although the
North American Stratigraphic Code (1983) advises
thoughtful consideration and a clear statement of need
before discarding a long-used name for an obscure ear-
lier one. An excellent review of lithologic terminology
and basic mapping procedures is given in ““Manual of
Field Geology” (Compton, 1985); the classic paper by
Schenck and Muller (1941) discusses the differences
between units of lithology (rocks), age (time), and
stage (time-rock). These authors used early, middle
and late subdivisions for age, and upper and lower
subdivisions for stage names.

Stratigraphic Terminology
Rock units: formation, member, group

The fundamental mappable unit is a formation,
whose name is based on a lithologic description and
includes a designated type section (also called the stra-
totype) from a specific geographic locality. In cases
where a single section is incomplete, a composite type
locality can be designated, as is recommended by Car-
reno et al. (2000) for the Tepetate Formation. A com-
plete description commonly includes lithologic varia-
tion, geographic extent, stratigraphic position, the na-
ture of upper and lower boundaries, age, paleontolog-
ical data if any, and prior nomenclatural history.
Names should not be preoccupied by formations else-
where within the country (North American Strati-
graphic Code, 1983, articles 7b and 7c).

A member is part of a formation, a lithologic unit
of lesser rank that is always defined as a subunit of a
formally named formation. It can be a lens, tongue, or
reef, a wedge-shaped extension of the main formation,
or a separate facies, such as the Cerro Colorado Mem-
ber of the El Cien Formation of Applegate (1986). A
bed (or beds) is the smallest lithostratigraphic division
of a sedimentary rock; it can be a distinctive marker,
such as the Capas Humboldt phosphorite bed at San
Juan de la Costa, or the Llajas de Palo Verde of Ojeda-
Rivera (1979), a local horizon at the top of the Cerro
Tierra Blanca Member of the El Cien Formation of
Applegate (1986). In volcanic rocks, a flow or a tuff

12 BULLETIN 371

is the equivalent of a bed, such as the Tuff of San
Felipe of Stock er al. (1999).

Group is the largest category of lithologic unit. It
consists of two or more associated formations or a col-
lection of named and undifferentiated lithologic units
that are associated or share aspects of age, composition
or history. An example from the Vizcaino embayment
is the Valle Group, which is composed of several for-
mations that were laid down in a similar depositional
setting between Cretaceous and Eocene time (D. P.
Smith et al., 1993a). The Poway Group, La Jolla
Group, and Rosario Group of the San Diego area were
originally described as formations but raised to Group
status to reflect similarities in lithology and origin of
the units that comprise them (Kennedy and Moore,
1971). The concept of a Group can be especially useful
in small-scale mapping and regional stratigraphic anal-

yses.

Time-rock units: stages and zones

Paleontologists use faunal stages to define packages
of rocks and structures such as unconformities that
represent a particular increment of geologic time. Fau-
nal or floral assemblages define zones by which stages
are recognized. They can be based upon diatoms (Bar-
ron, 1985, 1986; Barron ef al., 1985); foraminifers and
nannofossils (Bolli et al., 1985a,b; Mallory, 1959;
Kleinpell, 1938, 1980; Finger, 1990); mammals (Prot-
hero, 1995), or invertebrates (Squires et al., 1988;
Saul, 1983). Time-rock units are related to the geolog-
ic time scale and recognized by distinctive assemblag-
es of index species that range throughout the given
stage. The age of a rock, in contrast to its stage, is the
time period, usually measured in millions or hundreds
of thousands of years, during which the rock unit was
formed; it can be an “absolute” number based on ra-
diometric measures, such as 12.6 Ma for the Tuff of
San Felipe, or a general range construed from pale-
ontologic and stratigraphic constraints, such as late
Middle to Late Miocene for the Tortugas Formation.

Stages can be provincial, such as the Pacific Coast
Molluscan Stages, also called the West Coast Mollus-
can Stages (for example, the ““Capay” Stage for the
middle Early Eocene age sections of the Bateque For-
mation), or the broader European Stages (the Maas-
trichtian Stage for the Late Cretaceous age Rosario
Formation). Vertebrate paleontologists use North
American Land Mammal Stages (the Lower Arika-
reean Stage, Late Oligocene age Otay Formation of
the San Diego area, for example). Pacific Coast Mol-
luscan Stage names are not generally used for Neogene
formations in Baja California because many of the
Mexican species have closer faunal affinities with the

Tertiary-Caribbean province than with California Ter-
tary taxa, and they require further study.

The International Commission on Stratigraphic No-
menclature continually refines global stage correlations
based on particular stratigraphic sections. Their web
site provides up-to-date information on Global Bound-
ary Stratotype Sections and Points, such as the section
near Rabat, Morocco, that was named the standard for
the Miocene—Pliocene boundary (Benson and Rakic-
El Bied, 1996). Such data are especially useful in re-
fining the ages of a number of formations in Baja Cal-
ifornia that span the Miocene—Pliocene boundary;
these include the Almejas Formation, Tirabuz6n For-
mation, and Carmen Formation.

Stage boundaries commonly do not coincide with
age (epoch) or formation (lithologic) boundaries; stag-
es are useful for refining resolution and correlation be-
tween two formations, and distinguishing upper and
lower units within a formation of a given age. They
can indicate time transgressed by a formation that
varies in age Over its geographic extent. For example,
the Bateque Formation is middle Early Eocene in age,
“Capay” Stage south of Laguna San Ignacio, and late
Middle Eocene age, “Tejon” Stage at its southern oc-
currence at the mouth of Arroyo Mezquital (Squires
and Demetrion, 1992).

Informal lithologic units

We use lithologic names (Pliocene marine sand-
stone, basalt of Rancho Esperanza, unnamed volcani-
clastic sandstone, for example) for units that are un-
described or not yet well understood. Informal names
cited in this paper are not officially established by this
publication.

Taxonomic Note

Published papers dealing with the taxonomy of mi-
crofossils recovered from sedimentary or volcano-sed-
imentary strata of Baja California are scarce, although
some important publications use micropaleontology to
assign ages and/or interpret paleoenvironments of the
marine strata that contain them. Some of these papers
do not indicate a repository for the microfossils, but
many were placed in the National Museum of Natural
History (e.g., Pessagno, 1979, and Bukry, 198la) or
the California Academy of Sciences (e.g., Hanna,
1930; Hanna and Grant, 1926; Mandra and Mandra,
1972). Microfossils listed in a number of theses were
placed in the Micropaleontology Thesis Collection of
the School of Earth Science at Stanford University
(Boehm, 1982: Helenes-Escamilla, 1980, 1984; Kim,
1987) and at Rice University (Pérez-Guzman, 1983).
Specimens determined by Carreno (see references
herein) are housed in the Micropaleontology section of

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 13

the Paleontological Collection at the Instituto de Geo-
logia, Universidad Nacional Autonoma de Mexico,
Mexico, D.F, where they have IGM-Microfossil num-
bers.

Molluscan species cited herein were determined by
J. T. Smith from her collections made between 1979
and the present, and from well-illustrated type speci-
mens in the Tertiary marine molluscan literature. Spec-
imens from southern California and the Baja Califor-
nia peninsula were compared with the type and general
holdings of the California Academy of Sciences and

Leland Stanford Junior University, the University of

California Berkeley Museum of Paleontology, Natural
History Museum of Los Angeles County, San Diego
Museum of Natural History, the University of Chica-
go, the U. S. Geological Survey, and the National Mu-
seum of Natural History. Ongoing systematic research
includes redetermining earlier-named taxa that were
described from a single or only a few individuals from
a particular formation or basin. Many taxa have mul-
tiple synonyms that obscure their broader geographic
distributions. Current investigations consider variabil-
ity with growth stage and mode of preservation, re-
fined ages of fossiliferous units with respect to asso-
ciated radiometrically dated rocks, and species distri-
butions within a broader tectonostratigraphic context.
Preliminary results document a number of Tertiary-
Caribbean species in Baja California and southern Cal-
ifornia and permit closer correlation between marine
basins.

ACKNOWLEDGMENTS

The need for an updated correlation chart grew out
of biennial meetings in 1991, 1993, 1995, 1997, 2000,
and 2002 of the Peninsula Geological Society, or So-
ciedad Geologica Peninsular, which was founded in
1991 in La Paz, Baja California Sur. Our charts are
the result of many collaborations with all who share
an interest in the geology of Baja California. Col-
leagues who provided special encouragement and as-
sistance are: Douglas P. Smith, California State Uni-
versity, Monterey, California; Jorge Ledesma-Vaz-
quez, University of Baja California, Ensenada, Baja
California; Sergio Cevallos-Ferriz, Luis Espinosa-
Arrubarrena, and Shelton P. Applegate, Universidad
Nacional Aut6noma de Mexico, Mexico, D.E: John A.
Barron, Kristin McDougall, and James G. Smith of the
U.S. Geological Survey; Edward C. Wilson, formerly
of the Natural History Museum of Los Angeles Coun-
ty; Arturo Martin-Barajas, Luis Delgado-Argote, and
Javier Helenes, CICESE, Ensenada, Baja California;
James C. Ingle, Jr., Stanford University, Stanford, Cal-
ifornia; Tobias Schwennicke, Elvia Plata-Hernandez,
and Genaro Martinez-Gutieérrez, Universidad Autono-

ma de Baja California Sur; and Patricia A. Whalen,
University of Arkansas.

We thank the reviewers, LouElla Saul and Kristin
McDougall, for their helpful comments, and Edward
C. Wilson for reading a preliminary draft.

We gratefully acknowledge the field or laboratory
collaboration and assistance of the following: James
R. Ashby, Jr, Larry Barnes, Mark Boehm, Mike Cas-
sidy, Thomas Cronin, Thomas A. Démére, Rebecca
Dorsey, Roy Fulwider, Thomas Fumal, Gordon Gastil,
Joyce Gemmell, Gerardo Gonzalez-Barba, Luis Her-
rera-G., Susan Kidwell, Jorge Ledesma-Vazquez,
Claudia Lewis, Cecelia McCloy, Arturo Martin-Bara-

jas, Hugh McLean, John Minch, Jay Neuhaus, Sergio

Pedrin-Aviles, Gustavo Padilla-Arredondo, José Pérez-
Venzor, Ernesto Diaz-Rivera, Tom Rockwell, Raul Ro-
driguez-Quintana, Jaime Roldan-Quintana, Pete Sad-
ler, LouElla and Dick Saul, Tobias Schwennicke, Alle-
gra V. Smith, James G. Smith, Joann Stock, Miguel
Téllez-Duarte, Paul Umhoeter, Edward C. Wilson, and
Charles Winker. The Universidad Autonoma de Baja
California, Universidad Autonoma de Baja California
Sur, and the U. S. Geological Survey provided vehicles
and support for a number of collecting and reconnais-
sance trips.

Lindsey Groves and Harry Filkorn of the Natural
History Museum of Los Angeles County provided
type specimen and locality information. Many librar-
ians guided us to hard-to-find literature: Charlotte
Derksen and the staff of the Stanford University Bran-
ner Earth Sciences Library and Map Collections, Mar-
tha Rosen and David Steere of the Smithsonian Insti-
tution Libraries at the National Museum of Natural
History, and Thomas Carey of the San Francisco His-
tory Center, San Francisco Public Library. Natalie E.
Smith arranged for copies of rare literature from spe-
cial collections. We appreciate the advice of Joann
Sanner, National Museum of Natural History Depart-
ment of Paleobiology, and the technical assistance of
M. Alcayde-Orraca, Instituto de Geologia, Universidad
Nacional Aut6noma de Mexico. Preliminary text-fig-
ures were made by E A. Vega; final maps were drafted
in Adobe Illustrator by James G. Smith. The Direccion
General de Asuntos del Personal Académico provided
support through UNAM (Universidad Nacional Auto-
noma de Mexico) grant number INI102995. Jamie G.
Smith consulted on the photographic figures.

We especially acknowledge the kindness of the
ranchers of Baja California Sur, some of whom accom-
panied us into the field and shared detailed knowledge
of the terrain. They include: Senor Felipe Moreno,
Rancho el Refugio; Senor Enrique Fiol, Rancho la
Trinidad; Senor Juan Angel Alvarez, Rancho Algo-
dones; Senor Manuel Rubio-Hueso, Rancho la Fortu-

14 BULLETIN 371

na; and Senor Leonardo de la Toba, Rancho el Meé-
dano.

PART I: THE WESTERN BAJA CALIFORNIA
PENINSULA

SAN DIEGO, CALIFORNIA, TO
TODOS SANTOS, BAJA CALIFORNIA SUR

San Diego embayment
Geographic Overview

The San Diego embayment is an onshore Tertiary
marine basin similar to the Los Angeles, Ventura, San-
ta Barbara, and Santa Maria embayments of southern
California. It extends from north of Encinitas through
the greater San Diego area and across the international
boundary to several kilometers south of Playas de Ti-
juana and La Joya, Baja California. Structurally, this
embayment lies in a graben bounded on the east by
the La Nacion-Sweetwater fault system of Artim and
Pinckney (1973) and on the west by offshore faults
(Demére, 1983). Cretaceous, Eocene, and Pliocene
sediments of at least 1,100 m thickness overlie Me-
sozoic basement that includes metamorphic and gra-
nitic rocks (M. P. Kennedy, 1975; M. P. Kennedy and
G. W. Moore, 1971). The Tijuana basin of the northern
Rosarito embayment partly overlaps the San Diego
embayment. Both embayments le within the Califor-
nia Continental Borderland structural province. They
are bounded on the east by the Peninsular Ranges and
underlain by the same basement as the San Diego em-
bayment. Quaternary marine terrace deposits are found
along much of the coastal area.

San Diego embayment
Plate 1, Column |

Rancho Santa Fe, California, to La Joya,
Baja California, Mexico
(Text-figs. 2, 3, Table 1, Appendices 1, 2)

Column modified from M. P. Kennedy (1975) and
Ashby and Minch (1984). Area shown on Point Loma,
La Jolla, Del Mar, Encinitas, Rancho Santa Fe, Escon-
dido, Poway, La Mesa, and National City quadrangles,
California, and the Tijuana quadrangle, I11C69 and
111079, 1:50,000, Baja California. Geologic maps of
the area include California Division of Mines and Ge-

ology San Diego 2° sheet; M. P. Kennedy (1967), scale
1:24,000; Minch (1967); and M. P. Kennedy and G.
W. Moore (1971).

Stratigraphy

Mesozoic to Paleogene basement rocks.—The old-
est rocks in the area are the Santiago Peak Formation,
metamorphosed rocks of Jurassic age that crop out at
Black Mountain in the Poway quadrangle. They were
intruded by Cretaceous plutons known collectively as
the Peninsular Ranges batholith, which extends from
north of San Diego to 28°N.

The Santiago Peak Formation is overlain uncon-
formably by gently folded Late Cretaceous and Early
(?) to Late Eocene rocks that are discussed by M. P.
Kennedy and G. W. Moore (1971) and M. P. Kennedy
(1975). These authors raised a number of formation
names to group level, oldest to youngest: Rosario
Group, La Jolla Group, and Poway Group. Individual
formations, type locality, and age data are summarized
in Table | and shown in Text-figure 3 and Plate 1,
Column 1.

The Rosario Group, named for the Upper Creta-
ceous Rosario Formation, includes all the postbatho-
lithic Mesozoic units of the San Diego embayment.
Oldest to youngest, they are the Lusardi Formation,
Point Loma Formation, and Cabrillo Formation. They
are unconformably overlain by the Eocene La Jolla
Group of six intertonguing marine and nonmarine for-
mations, all nearly flat-lying and described from the
coastal San Diego area. From oldest to youngest these
are: Mount Soledad Formation, Delmar Formation,
Torrey Sandstone, Ardath Shale, Scripps Formation,
and Friars Formation. They are overlain by three Late
Eocene Poway Group nonmarine formations: the Sta-
dium Conglomerate, Mission Valley Formation, and
Pomerado Conglomerate. An angular unconformity
separates them from the overlying late Neogene San
Diego Formation.

San Diego Formation, Late Pliocene—Early Pleis-
tocene.—The area trom Pacific Beach, north of San
Diego, to La Joya, south of Tijuana, is underlain by
discontinuous outcrops of the San Diego Formation, a
fossiliferous marine Pliocene to Early Pleistocene unit
named for a section along the sea cliffs at Pacific

Text-figure 3.—Quadrangles of the San Diego embayment and northern Rosarito embayment (= northern Tijuana basin). Eastern boundary
of the San Diego embayment is from M. P. Kennedy (1975). Open circles mark type sections of units described from this area (Table 1): 1,

Lusardi Formation; 2, Delmar Formation;

3, Torrey Sandstone; 4, Scripps Formation: 5, Ardath Shale; 6, Mount Soledad Formation; 7, Poway

Conglomerate; 8, Pomerado Conglomerate; 9, San Diego Formation; 10, Friars Formation; 11, Stadium Conglomerate; 12, Mission Valley
Formation; 13, Point Loma Formation; 14, Cabrillo Formation; 15, **Black Mountain Volcanics”; 16, Otay formation, informal name; 17,

Sweetwater Formation.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

33° 07' 30" N

°152' 30" W

Carlsbad °107' 30" W

Encinitas
33° 00'N

32° 52' 30" N

Sweetwater
Reservoir

ANOZ Linvy no\o™

Point
Loma 2
\ National City

Chula Vista

@ Tijuana

a Joya
‘oo. Ww La Presa

Tijuana 117

BULLETIN 371

Table 1.—San Diego embayment, lithostratigraphic units (Text-fig. 3). Lowercase names indicate informal units that were not established
according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Ardath Shale

Bay Point Formation

Cabrillo Formation

Delmar Formation

Friars Formation

La Jolla Group

Lindavista formation

Lusardi Formation

Mission Valley Forma-
tion

M. A. Hanna (1926) named as
member of Rose Canyon
Shale; M. P. Kennedy and G.
W. Moore (1971) raised to for-
mation in La Jolla Group.

Hertlein and Grant (1939).

M. P. Kennedy and G. W. Moore
(1971) named as formation in
Rosario Group.

M. A. Hanna (1926) named the
Delmar Sand as member in La
Jolla Formation of Clark
(1926); M. P. Kennedy and G.
W. Moore (1971) raised to for-
mation in La Jolla Group.

M. A. Hanna (1926) included in
Rose Canyon Shale Member of
the La Jolla Formation of Clark
(1926); M. PB. Kennedy and G
W. Moore (1971) raised to for-
mation in La Jolla Group.

Clark (1926) named as Forma-

tion; M. P. Kennedy and G. W.

Moore (1971) raised to group
that includes Mount Soledad
and Delmar Formations, Tor-
rey Sandstone, Ardath Shale,
Scripps and Friars Formations.

M. A. Hanna (1926) called a ter-
race, not a formation; not a
formal rock unit.

Nordstrom (1970) named as for-
mation; M. P. Kennedy and G.
W. Moore (1971) included in
Rosario Group.

M. P. Kennedy and G. W. Moore
(1971) named as part of Po-
way Group.

Unit is an olive-gray silty shale with thin beds of sandstone, concre-
tions, and molluscan fossils. Type section is 70-m-thick, on the east
side of Rose Canyon 800 m south of the junction of Ardath Road
and Interstate 5, La Jolla 74-minute quadrangle. Early Middle Eo-
cene age (Bukry and M. P. Kennedy, 1969).

yrmation is a widespread fossiliferous marine to nonmarine sand-
stone described from the coastal San Diego area, California (M. P.
Kennedy, 1975). Kern (1971) regarded it as a late Pleistocene (San-
gamon) estuarine deposit that interfingers with a nonmarine slope

wash. Molluscan index species are Late Pliocene or Early Pleisto-
cene (G. L. Kennedy, 1973).

Massive sandstone, thin siltstone beds, and massive crossbedded cob-
ble conglomerate with diorite clasts exposed in 81-m-thick type
section on the Point Loma peninsula, 250 m east of the lighthouse,
Point Loma 7!2-minute quadrangle; also crops out at Pacific Beach
and La Jolla. Contains the Cretaceous age, Maastrichtian Stage bi-
valve, ““Pharella” alta (Gabb) (L. R. Saul in M. P. Kennedy,

1975).

Unit is a lagoonal deposit of sandy claystone interbedded with coarse-
grained sandstone and well-indurated brackish-water oyster beds
composed of Ostrea idriaensis Gabb. Described from a canyon two
Kilometers south of the Del Mar railroad station in the Del Mar
7¥2-minute quadrangle, and mapped from the subsurface as far
north as Carlsbad (M. P. Kennedy, 1975). Partly equivalent to the
overlying Torrey Sandstone. Middle Eocene, Domengine West
Coast Molluscan Stage.

Formation includes a nonmarine and lagoonal sandstone and greenish-
gray claystone described from a 35-m-thick section on the north
side of Mission Valley near Friars Road, La Jolla 7/2-minute quad-
rangle. Contormably overlain by the Stadium Conglomerate. Mid-
dle to Late Eocene age based on a brontotheriid tooth and the ages
of associated members.

La Jolla Formation was described from La Jolla; many of the other
units were described by M. A. Hanna as part of his Rose Canyon
Shale Member of the La Jolla Formation. Middle Eocene age; these
formations correlate with the Delicias and Buenos Aires Formations
of the Tijuana basin, Baja California (Flynn, 1970).

Nearshore marine and nonmarine terrace deposits of reddish-brown
interbedded sandstone and conglomerate with reworked Poway
Conglomerate clasts seen along the Lindavista Railroad siding in
the La Jolla quadrangle (M. P. Kennedy, 1975). Contact with the
underlying San Diego Formation uncontormable or gradational, in-
terpreted as a regressive phase of the upper part of the San Diego
Formation (Peterson and Jefferson, 1971). Early Pleistocene.

Unit includes boulder and cobble conglomerates with sandstone lenses
exposed in the Rancho Santa Fe quadrangle at the confluence of
Lusardi Creek and the San Dieguito River, three kilometers south-
east of Rancho Santa Fe, in the quadrangle of the same name (M.
P. Kennedy, 1975). Reported from subsurface wells at Point Loma
Peninsula and overlain unconformably by the basal Point Loma
Formation (G. L. Kennedy and others, 2000), Correlative with the
Redondo Formation of Flynn (1970) in northern Baja California
(Ashby, 1989a,b). Late Cretaceous.

Formation is predominantly fine-grained fossiliferous marine sand-
stone with a sandstone layer containing silicified wood and a cob-
ble-conglomerate facies. Type section is exposed on the west side
of Highway 163 along the south wall of Mission Valley in San Di-
ego, La Mesa 72-minute quadrangle. Unit thins from west to east,
ends in the eastern Poway and La Mesa 72-minute quadrangles. Late
Eocene megafossils in the uppermost beds (M. P. Kennedy, 1975).

Table 1.—Continued.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH Ls

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Mount Soledad Forma-
tion

Point Loma Formation

Pomerado Conglomer-
ate

Poway Conglomerate
or Poway Group

Rosario Group

San Diego Formation

Santiago Peak Forma-
tion

Scripps Formation

M. P. Kennedy and G. W. Moore
(1971) named as part of La
Jolla Group.

M. P. Kennedy and G. W. Moore
(1971) named as formation in
Rosario Group.

G. L. Peterson and M. P. Kenne-

dy (1974) named as formation:

M. P. Kennedy and G. W.
Moore (1971) included in Po-
way Group.

Ellis (1919) named; M. P. Ken-
nedy and G. W. Moore (1971)
raised to Poway Group, which
includes all the rocks above
the La Jolla Group and below
the San Diego Formation: Sta-
dium Conglomerate, Mission
Valley Formation, and Pomer-
ado Formation.

M. P. Kennedy and G. W. Moore
(1971) raised Rosario Forma-
tion to Rosario Group, which
includes all Late Cretaceous
post-batholithic rocks in San
Diego County.

Dall (1898) and Arnold (1903),
early references to the name:
Arnold (1906) refined.

Larsen (1948) renamed preoccu-
pied “Black Mountain Volca-
nics” of M. A. Hanna (1926).

M. P. Kennedy and G. W. Moore
(1971) named, included in La
Jolla Group.

Unit is marine cobble conglomerate and sandstone named for a type
section on Mount Soledad, at the head of an amphitheater 400 m
west of the intersection of Ardath Road and Interstate 5 in the La
Jolla 72-minute quadrangle. It crops out at Pacific Beach and south
of Mission Bay; it overlies the Cabrillo Formation unconformably.
Middle Eocene (Demere, 1983).

Type section is marine sandstone and siltstone exposed along sea
cliffs at the tip of the Point Loma peninsula, San Diego County. It
crops out in La Jolla and correlates with the middle part of the Ro-
sario Formation in northern Baja California (M. P. Kennedy, 1975).
Late Cretaceous age, Campanian—Maastrichtian Stage microfossils
(Shiter, 1968, 1984),

Unit is a 10-m-thick nonmarine cobble conglomerate named for a
type section along Pomerado Road on the divide between Carroll
Canyon and Poway Valley, eastern Poway 7'2-minute quadrangle.
Late Eocene age, based on its relation to the underlying Mission
Valley Formation (M. P. Kennedy, 1975).

Unit is an alluvial conglomerate, sand and shale described from a sec-
tion along the south wall of Poway Valley, Poway 7’2-minute quad-
rangle. The Late Paleocene to Late Eocene deposits contain distinc-
tive rhyolite and dacite clasts derived from a source area near El
Plomo, Sonora, in northern Mexico (Abbott and T. E. Smith, 1989).
Poway clasts are also present in deep marine conglomerates on the
Northern Channel Islands, where they are important markers for the
reconstruction of the California Continental Borderland (Abbott er
al., 1983).

Group is based on the Late Cretaceous Rosario Formation formally
described from the area of El Rosario, Baja California, 300 km
south of the International boundary (Santillan and Barrera, 1930).
The Group includes (oldest to youngest) the Lusardi, Point Loma
and Cabrillo Formations; it crops out from San Diego to Ensenada,
Baja California.

Unit includes a basal pebble to cobble marine conglomerate overlain
by gray to yellow sandstone, silty sandstone and conglomerate;
above this is a fossiliferous, silty, bioturbated sandstone. Type sec-
tion is a 74-m-thick package of Late Pliocene fossiliferous sedi-
ments (Demére, 1983) in the sea cliffs at Pacific Beach, La Jolla
72-minute quadrangle (Arnold, 1903). Dominantly marine sedi-
ments crop out from Mount Soledad near Pacific Beach to La Joya,
Baja California, and as far east as Otay Mesa (Artim and Pinckney,
1973). Many workers at different locations recognized two mem-
bers: a lower Late Pliocene fine-grained sandstone and an upper,
latest Pliocene to Early Pleistocene sandstone and conglomerate
that grades up section to nonmarine sediments. Age ranges from
Late Pliocene to Early Pleistocene (Demere, 1983).

Prebatholithic, slightly metamorphosed volcanic, volcaniclastic, and
sedimentary rocks were described from Black Mountain in the
northwestern Poway 7’2-minute quadrangle. Adams and Walawen-
der (1982) summarized stratigraphic and age data for the unit,
which crops out for 130 km from the Santa Ana Mountains in
Orange County, California, to central Baja California (M. P. Kenne-
dy and G. L. Peterson, 1975). Latest Jurassic age, Portlandian
Stage, based on the index species Buchia piochit (Gabb), the bel-
emnoid Cylindroteuthis sp., and lead-alpha ages of 150 and 155 +
10% on a metarhyolite and a metadacite, respectively (Jones and
Miller, 1982; Bushee er al., 1963).

Type section is a sandstone with cobble conglomerate and siltstone
interbeds described from a kilometer north of the Scripps Pier,
north side of Black’s Canyon, La Jolla 742-minute quadrangle. The
unit is also exposed from east of Del Mar to south of the mouth of
Mission Valley. Middle Eocene (M. P. Kennedy, 1975).

18 BULLETIN 371

Table |.—Continued.

Lithostratigraphic unit Author, reference

Lithologic description, type locality, age

Stadium Conglomerate M. P. Kennedy and G. W. Moore
(1971) named in Poway

Group.

M. A. Hanna (1926) named as
Member of La Jolla Formation
of Clark (1926); M. P. Kenne-
dy and G. W. Moore (1971)
raised to formation of La Jolla
Group.

Torrey Sandstone

Unit is a massive cobble and boulder conglomerate that contains dis-
tinctive slightly metamorphosed volcanic and volcaniclastic Poway
clasts. Type section is in the northern wall of Mission Valley
(along Interstate 8 near the San Diego Stadium), at the boundary
between the La Jolla and La Mesa 742-minute quadrangles. It crops
out from east of Del Mar to south of the mouth of Mission Valley.
Middle (?) and Late Eocene (M. P. Kennedy and G. W. Moore,
1971).

White to light brown arkosic sandstone interfingers with and grades

into the overlying transgressive Ardath Shale. Type section is on
the Torrey Pines Grade of Highway 101 where it climbs from Sole-
dad Valley to the south, in the La Jolla 74-minute quadrangle.
Middle Eocene, based on its association with the well-dated, inter-
fingering Ardath Shale.

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Text-figure 4.—Rosarito embayment, Tijuana basin in the north
and La Mision basin in the south. Map modified from Ashby
(1989b). Open circles indicate type sections: 1, Otay formation, in-
formal name; 2, Sweetwater Formation; 3, Rosarito Beach Forma-
tion; 4, Buenos Aires Formation; 5, Delicias Formation; 6, Redonda
Fault abbreviations: LNE La Nacion Fault; LBR Los
Buenos Fault; ACF Agua Caliente Fault. La Gloria is east of the
Agua Caliente Fault and west of La Presa.

Formation.

Beach. Hertlein and Grant (1944) reported a total
thickness of 375 m (1,250 ft) for the formation in the
Chula Vista and San Ysidro areas; Minch (1967) cal-
culated only 85 to 90 m for the section near Tijuana,
the same thickness determined by Demeéré (1983) for
the basin as a whole. The northernmost outcrops are
west of the Rose Canyon Fault; southernmost expo-
sures are north of the Agua Caliente Fault (Demére,
1983) near La Joya (Text-fig. 4). The unit caps Otay
Mesa in southern San Diego County, where it overlies
Cretaceous and Eocene marine units of the northern
Tijuana Basin.

Early records, geologic setting, paleontological, and
lithological data for the San Diego Formation were
summarized by Deméré (1983). Several workers rec-
ognized two members, a lower Late Pliocene fine-
grained sandstone and an upper member of latest Pli-
ocene to Early Pleistocene sandstone that includes
cooler water fossils and grades upsection to nonmarine
sediments. In addition to mollusks, sand dollars, and
microfossils, the lower member has a rich vertebrate
fauna that includes whales, dolphins, sea lions, birds,
bony fishes, and sharks of the Blancan Land Mammal
Stage (Deméré, 1983).

Age and correlation of the San Diego Formation.—
Studies at La Joya suggest that the San Diego For-
mation is Late Pliocene in age (Ashby and Minch,
1984; Aranda-Manteca and Téllez-Duarte, 1989); the
section correlates with the “lower member” of the unit
in San Diego County as well as to the Niguel For-
mation of southern California (Deméré, 1983). Many
of the lower member megafossils are also found in the
upper part of the Almejas Formation of the Vizcaino
Peninsula, 700 km (440 mi) to the south, as well as in
Late Pliocene formations in the Los Angeles, Ventura
and Santa Maria basins to the north. Representative
Pliocene taxa include Pecten (Pecten) bellus Conrad,

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 19

Lituyapecten dilleri: (Dall), Lyropecten cerrosensis
(Gabb), Miltha xantust (Dall), and the colonial bar-
nacle Balanus gregarius (Conrad). Demeré (1983) not-
ed that planktonic foraminifers correlated with data
from the Deep Sea Drilling Project suggest the San
Diego Formation in the Mount Soledad area is as
young as the Early Pleistocene Emiliania annula Sub-
zone, approximately 1.5 Ma.

Tijuana basin, northern Rosarito embayment
Plate 1, Column 2

EastLake Development, San Diego County,
California, through Rosarito to Punta Descanso,
Baja California
(Text-figs. 2, 4, Table 2, Appendices 1, 2)

Column modified from Flynn (1970), Ashby
(1989a,b), Demeré (1988), and Walsh and Demeéreé
(1991). The area is shown on the Jamul Mountains 7!2-
minute quadrangle, southwestern San Diego County,
California; the Tijuana quadrangle I-11 C69 and I-11
C79; the La Presa quadrangle I-11D71, Baja Calitor-
nia, 1:50,000; and the geologic maps of Flynn (1970)
and Artim and Pinckney (1973).

Overview

The Rosarito marine embayment (Text-fig. +) exist-
ed from the Late Cretaceous to Late Pliocene; it in-
cluded the northern Tijuana basin (the EastLake De-
velopment, east of Chula Vista, California, to Punta
Descanso, Baja California) and the southern La Mision
basin, from Punta Ventanita to Punta San Miguel, 10
km northwest of Ensenada (Ashby, 1989b). The strati-
graphic units described from these areas are generally
correlative, but no member of the Rosarito Beach For-
mation is present in both basins. Formations, their au-
thors, type sections, and brief descriptions are tabulat-
ed in Table 2.

Stratigraphy

Mesozoic units.—Mesozoic prebatholithic metamor-
phic and volcanic basement rocks and the Peninsular
Ranges batholith were discussed by Gastil ef al.
(1975). They are overlain unconformably in north-
western Baja California by the Late Cretaceous Re-
donda Formation, a massive unfossiliferous conglom-
erate and breccia (Flynn, 1970), and by unconformable
marine sediments of the Late Cretaceous Rosario For-
mation. Yeo (1984) and Ashby (1989a,b) correlated
the Redonda Formation with the Lusardi Formation of
the northern San Diego embayment.

Delicias and Buenos Aires Formations, Eocene.
Flynn (1970) mapped the La Gloria-Presa Rodriguez
(or La Presa) area southeast of Tijuana, where he de-

scribed the Early to Middle Eocene Delicias Forma-
tion, which correlates with the Del Mar Sandstone of
the La Jolla Formation in San Diego County. He also
described the unconformably overlying marine Buenos
Aires Formation of Middle to Late Eocene age.

Sweetwater Formation, Late Eocene. Otay forma-
Northwest of
the Presa Rodriguez-La Gloria region the international
boundary area is underlain by the nonmarine Late Eo-
cene Sweetwater Formation and Late Oligocene Otay
formation, both described from southern San Diego
County (Artim and Pinckney, 1973) and revised by
Walsh and Demére (1991). Although they are non-
marine, they are included in the northernmost Tijuana
basin because their type areas lie east of the San Diego
embayment.

Before the vertebrate fossil localities were discov-
ered, the nonmarine clastic rocks were mapped togeth-
er as Miocene sediments. Later, the lower beds were
recognized as the Sweetwater Formation of Late Eo-
cene age based on Uintan and/or Duchesnean Stage
land mammals (Walsh and Demeéreé, 1991). The con-
glomeratic and gritstone facies that were formerly in-
cluded in the upper part of the section were remapped
as disconformable and referred to the Otay formation
(informal name). Otay formation vertebrate fossils,
termed the “‘EastLake local fauna” by Deméré (1988),
include a number of Late Oligocene age, Lower Ari-
kareean Stage mammals such as the oreodont Sespia,
a few reptiles, and birds.

Publications prior to 1988 commonly included or
correlated the Otay formation with the Miocene Ro-
sarito Beach Formation of Minch (1967), but the
**EastLake local fauna” is considerably older. The ver-
tebrates correlate the unit with the Tecuya Formation
of the San Emigdio Mountains and the upper Sespe
Formation in southern California, and with the John
Day Formation of Oregon (Deméré, 1988).

tion, informal name, Late Oligocene.

Rosarito Beach Formation, Middle to Late Mio-
cene.—Minch (1967) and Minch er al. (1984) de-
scribed the Rosarito Beach Formation and a number
of members from the Rosarito area in the Tijuana ba-
sin. Oldest to youngest they are: Mira al Mar, Costa
Azul, Amado Nuevo, Las Glorias and Los Buenos
Members. Their authors and type sections are listed in
Table 2. The Mira al Mar unit yielded Middle Miocene
marine fossils, including diatoms (Scheidemann and
Kuper, 1979) and mollusks (Minch, 1967) that corre-
late it with the Los Indios Member of the La Mision
basin to the south (Ashby, 1989a,b). The Costa Azul
Member includes a basalt with a K/Ar age of 14.3 +
2.6 Ma (Hawkins, 1970).

BULLETIN 371

Table 2.—Rosarito embayment, Tijuana and La Mision basins, lithostratigraphic units (Text-fig. +). Lowercase names indicate informal units
that were not established according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit/

Basin

Author, reference

Lithologic description, type locality, age

Amado Nuevo Mem-
ber/Tijuana basin

Buenos Aires Forma-
tion/Tijuana basin

Costa Azul Member/
Tijuana basin

Delicias Formation/
Tijuana basin

Descanso member,
informal name/La
Mision basin

La Mision Member/
La Mision basin

Las Glorias Member/
Tijuana basin

Los Buenos Member/
Tijuana basin

Los Indios Member/
La Mision basin

Medio Camino mem-
ber, informal name/
La Mision basin

Minch (1967) described as mem-
ber in Rosarito Beach Forma-
tion,

Flynn (1970).

Minch (1967) named as member
in Rosarito Beach Formation.

Flynn (1970)

Ashby (1989a,b) used name in-
formally as part of Rosarito
Beach Formation.

Minch er al. (1984) named as
member of Rosarito Beach
Formation.

Minch (1967) described as mem-
ber of Rosarito Beach Forma-
tion.

Minch (1967) named as member
of Rosarito Beach Formation.

Minch er al. (1984) named as
member of Rosarito Beach
Formation. Ashby (1989a,b)
mapped type area and mea-
sured sections.

Ashby (1989a,b) used name in-
formally as member of Rosari-
to Beach Formation.

Unit consists of massive to scoriaceous basalts with a thick ash bed
100 ft above the base. It crops out north of Rosarito Beach approx-
imately 2.5 km south of Escuela Amado, on north slope of large
canyon near the Agua Caliente Fault, El Rosarito quadrangle, Baja
California. Miocene,

ormation has two members: a lower 70-m-thick cobble to boulder

conglomerate with sandstone and mudstone matrix, and an upper 60-

to 8O-m-thick white to tan marine fossiliferous sandstone that grades

laterally to arkosic sandstone and mudstone. Type section is in the

La Gloria-La Presa Rodriguez area southeast of Tijuana (Text-fig. 4,

area between La Presa and the Agua Caliente Fault). It is exposed

on the grade leading trom Valle Cuero de Venado toward Rancho

Buenos Aires, La Presa quadrangle. Unit crops out from Rancho De-

licias to the mesas of the Sierra Juarez and overlies the Delicias For-

mation with unconformity. Middle to Late Eocene.

Member consists of basalt and tuffaceous interbeds. Type area is in-
land from La Joya, Baja California, El Rosarito quadrangle; it ex-
tends from 90 m (300 ft) due east of Rancho José to the ridge top,
mostly west of the Los Buenos Fault, Miocene, based on a basalt
dated at 14.3 + 2.6 Ma (Hawkins, 1970).

Formation has two members, a lower mudstone and an upper sand-
stone, named from the La Presa quadrangle, Baja California. Type
section for the lower member is 4 km southeast of Rancho Delicias
on the grade below Rancho Buenos Aires; the upper member was
described from an amphitheater south of Rancho Delicias, S—6 km
southwest of Mexico 2 between Tijuana and Tecate, Baja Califor-
nia. Early to Middle Eocene.

Member 1s a mesa-capping conglomerate that is well-exposed on the
northeast corner of Mesa de los Indios northeast of La Mision,
Measured type section is well-described in Ashby (1989a) from

.. those exposures on the slope near the gate on the road to the
top of Mesa de los Indios, just north of Juncalito,” Primo Tapia
quadrangle. Interbedded with, also overlies, upper part of the Los
Indios Member of the Rosarito Beach Formation. Middle Miocene.

Basalts and tuffs of the southern outcrop area of the Rosarito Beach
Formation were named from a type section on the old Highway 1
grade south of the town of La Mision, Primo Tapia quadrangle.
Lower part consists of olivine basalt flows that overlie the Rosario
Formation; the upper porphyritic basalt flow was dated at 16.1 +
2.1 Ma (Gastil er al., 1975). Both facies thin to the east. Early
Middle Miocene.

Member consists of tuffaceous sandstones and siltstones interlayered
with basalts. Type section is just north of Rosarito Beach near the
head of the highway grade, approximately 2 km, 375° W of the
town of Las Glorias, El Rosarito quadrangle. Late Middle Miocene.

Unit consists of olivine basalts, pyroclastic, and clastic sediments that
include thin sandstone and siltstone interbeds and a tuff layer at the
top. Type section is in the El Rosarito quadrangle west of Escuela
los Buenos, on the north side of the canyon. The youngest member
of the Rosarito Beach Formation is Miocene.

Member consists of abundantly fossiliferous marine and nonmarine
volcaniclastic sediments and tuffs. Type section is in a quarry ap-
proximately 64% km northeast of La Mision at the southwest end of
Mesa de los Indios, Primo Tapia quadrangle. Its large, diverse ver-
tebrate assemblage was termed the “La Mision Local Fauna” (De-
meéré ef al., 1984). Middle Miocene, constrained by an overlying
volcanic unit dated at 14.3 + 2.6 Ma (Hawkins, 1970), and a por-
phyritic basalt flow in the underlying Medio Camino Member dated
at 16.1 + 2.1 Ma (Gast er al., 1975; Minch et al., 1984).

Type section of tuff, basalt, and sandstone is exposed at Medio Cami-
no along the beach between Punta Mezquite and Canon El Descan-
so, Primo Tapia quadrangle. It underlies the Middle Miocene La
Mision Member, which contains a porphyritic basalt flow dated at
16.1 + 2.1 Ma (Gastil er al., 1975).

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH pA|

Table 2.—Continued.

Lithostratigraphic unit/

Basin

Author, reference

Lithologic description, type locality, age

Mira al Mar Member/
Tijuana basin

Otay formation, infor-
mal name/Tijuana
basin

Punta Mesquite mem-
ber, informal name/
La Mision basin

Redonda Formation/
Tiyuana basin

Rosario Formation/
Tijuana and La Mi-
sion basins

Rosario Group/
San Diego to Ensen-
ada. Tijuana and La
Mision basins

Rosarito Beach Forma-
tion/Tijuana and La
Mision basins

San Diego Formation/
San Diego embay-
ment and northern
Tijuana basin

Sweetwater Formation,
informal name/
Northern Tijuana ba-
sin

Minch (1967) named as member
of Rosarito Beach Formation.

Artim and Pinckney (1973) did
not formally designate a type
section. Walsh and Demere
(1991) measured sections and
described (oldest to youngest)
three intormal members: con-
glomerate, gritstone, and sand-
stone-mudstone members.

Ashby (1989a,b) used as lowest
member of Rosarito Beach
Formation.

Flynn (1970).

Anonymous (1924: 421) used but
did not describe; Santillan and
Barrera (1930) designated for-
mally.

M. P. Kennedy and Moore
(1971) named Group, which
includes (oldest to youngest)
the Lusardi, Point Loma, and
Cabrillo Formations.

Minch (1967) described the for-
mation and five members from
the Tijuana basin, named five
other members from the La
Mision basin.

Dall (1898) and Arnold (1903)
made early references to unit;
Arnold (1906) refined (Table
1).

Artim and Pinckney (1973) men-
tioned; Scheidemann and Ku-
per (1979) described a type
section; Walsh and Demeére
(1991) redefined unit.

Unit is a fossiliferous sandstone, limestone, and breccia. Type section
is on the north slope of the second canyon near Rancho Mira al
Mar, 8 km (0.5 mi) due south of the rancho, El Rosarito quadran-
gle. Ashby (1989b) correlated it with the Los Indios Member, the
Topanga Formation of the Los Angeles basin, and the Round
Mountain Silt of the San Joaquin Valley, California. Middle Mio-
cene.

Unit consists of fossiliferous nonmarine volcanic and volcaniclastic
rocks that crop out east of the La Nacion Fault and on Otay Mesa
in the San Diego embayment and in the northern part of the Tijua-
na basin. Mapped east of Chula Vista in the Jamul Mountains 7%-
minute quadrangle, the formation extends from 13 km north of the
international boundary to an undetermined distance south of it. De-
meéré (1988) listed 24 terrestrial vertebrate taxa, including mam-
mals, reptiles, and birds, as the ““EastLake Local Fauna” of Late
Oligocene, Early Arikareean Land Mammal Age (approximately
Ma). Fossils correlate these rocks with the nonmarine Tecuya For-
mation and upper Sespe Formation of California and the John Day
Formation of Oregon.

Breccias and tufts in the Primo Tapia quadrangle deposits were
mapped for 142 km along the beach south of Punta Mesquite, just
south of 32°10’ N and east of 116°55' W. Late Early or early Mid-
dle Miocene, uncontormable on basement rocks.

Unit is a massive unfossiliferous conglomerate and breccia that was
described from northwest of Gran Mesa Redonda in the La Gloria-
Presa Rodriguez area, east of the Agua Caliente Fault. Type section
is in Arroyo Rosarito, La Presa quadrangle, where it unconform-
ably overlies the Peninsular Ranges batholith and underlies the Ro-
sario Formation. Late Cretaceous.

Unit is a post-batholithic marine sandstone, shale, and conglomerate
described trom near the coastal town of El Rosario in the quadran-
gle of the same name (Table 3). Flynn (1970) mapped it in the La
Gloria-Presa Rodriguez area as a 75-m-thick lower arkosic sand-
stone with mudstone interbeds and an upper 45-m-thick gray to
green mudstone containing Campanian to Maastrichtian Stage mol-
lusks and microfossils. Late Cretaceous.

Group name based on the Rosario Formation described from the
southern Rosario embayment near the town of El Rosario, Baja
California (Table 3), Late Cretaceous.

Formation consists of interbedded basalt flows, pyroclastic rocks and
clastic sediments that as a whole extends from south of Tijuana to
Punta San Miguel, 10 km northwest of Ensenada, and offshore on
Islas Los Coronados and Isla Todos Santos. Type section is in the
Rosarito area south of Tijuana. Unit is underlain unconformably by
Eocene rocks, overlain by Pliocene sandstone and conglomerate of
the San Diego Formation. Mostly Middle Miocene in the Tijuana
basin, latest Early Miocene to Middle Miocene in the La Mision
basin.

Demereé (1983) reviewed the long history of this Plio—Pleistocene,
largely marine unit, whose southernmost outcrops are in the Tiyua-
na basin at La Joya.

Formation at its type section consists of a lower 42-m-thick fluvial

and lacustrine mudstone with sandstone lenses that interfingers with
a gritstone facies; it is overlain by a 35-m-thick red claystone
(Scheidemann and Kuper, 1979). Type section is east of Chula Vis-
ta and Otay Mesa, southeastern Jamul Mountains 72-minute quad-
rangle. It extends from 33 km north of the international boundary
to an unknown distance south. Originally regarded as Miocene and
mapped with the other nonmarine sediments, until Walsh and De-
mere (1991) identified the fossil vertebrates as Late Eocene, latest
Uintan and/or Duchesnean Land Mammal Ages, 37—42 Ma.

De, BULLETIN 371

San Diego Formation, Pliocene to Early Pleisto-
cene.—Fossiliferous sandstone and conglomerate of
the San Diego Formation overlie the Rosarito Beach
Formation with angular unconformity. Deméré (1983)
regarded its age in the La Joya area as Pliocene—Pleis-

tocene in this area (Table 1).

La Mision basin, southern Rosarito embayment
Plate 1, Column 3

Punta Ventanita through La Mision to
Punta San Miguel, Baja California
(Text-figs. 2, 4, Table 2, Appendices 1, 2)

Column from Ashby (1989a,b), Minch er al. (1984).
Area shown on the Primo Tapia, [1 1D81, and El Sau-
zal de Rodriguez, H11B11, quadrangles, 1:50,000; and
the geologic map of Ashby (1989a), scale 1:50,000.

Overview

The southern part of the Rosarito embayment ex-
tends from Punta Ventanita, 15 km north of La Mision
and the Guadalupe River Valley, to Punta San Miguel,
10 km northwest of Ensenada, Baja California. The
area is important to the tectonic and sedimentary his-
tory of northwestern Baja California because it con-
tains the type sections of Miocene sedimentary units
whose source areas alternated from east to west and
then east (Ashby, 1989a,b). Basement rocks are the
same as in the Tijuana basin; they are overlain by the
Rosario Formation, which was described from the next
embayment to the south.

Stratigraphy

Rosarito Beach Formation, Early to Middle Mio-
cene.—The La Mision area lies 75 km by toll road
south of Tijuana and includes the type sections of five
members of the Rosarito Beach Formation, an Early
to early Middle Miocene marine unit that was de-
scribed by Minch (1967) and further discussed by
Ashby (1989a,b) and Minch er al. (1970, 1984). The
five formally and informally described members crop
out on or near Mesa de los Indios, east of the coastline
and northeast of La Mision, Baja California. They are
unconformable on prebatholithic and batholithic base-
ment rocks, and on the Upper Cretaceous Rosario For-
mation. Berry and Ledesma-Vazquez (1997) recog-
nized a waxy olive gray mudstone containing signifi-
cant quantities of volcanic ash in the La Mision area:
further work is needed to determine whether it is a
new formation or a new, lowest member of the Ro-
sarito Beach Formation.

From oldest to youngest, the members of the Ro-
sarito Beach Formation in the La Mision basin are:
Punta Mesquite, Medio Camino, La Mision, Los In-

dios, and Descanso. Some of these are informal names
because full descriptions and type section designations
are unpublished (see Table 2).

Correlation

The most important members of the Rosarito Beach
Formation for correlation are the La Mision Member,
which contains a basalt flow dated at 16.1 + 2.1 Ma
(Gastil, 1975) and the Los Indios Member, which con-
tains abundant upper ““Temblor’” Stage marine mega-
fossils and Luisian Stage benthic foraminifers (15—13
Ma). These fossils include species present in the To-
panga Formation of the Los Angeles basin, the Round
Mountain Silt of the San Joaquin Valley, California,
and the Mira al Mar Member of the Tijuana basin
(Ashby, 1989a,b). The Los Indios Member vertebrates
represent the Hemingfordian Land Mammal Stage
(Deméré er al., 1984). The molluscan index species
Turritella ocoyana Conrad of authors has been used
to correlate the member with the Tortugas Formation,
Member A of Helenes-Escamilla (1980), of the Viz-
camino embayment.

Rosario embayment
Plate 1, Columns 4, 5, 6, 7

Ensenada to 28° N, state line between
Baja California and Baja California Sur
(Text-figs. 2, 5, 6)

Overview

South of Ensenada the Punta Banda Peninsula pro-

jects into Todos Santos Bay, a well-known stop on

field trips because of the fossiliferous outcrops of the
Cretaceous Rosario Formation and La Butadora, the
gigantic blowhole on the southwest side. Punta Santo
Tomas, Punta China, and the mouth of Rro Santo To-
mas are 25 km to the south. The Agua Blanca Fault
Zone, which trends northwest on the northeast side of
Punta Banda, marks the northernmost occurrence of
the Alisitos Formation, an extensive arc-derived vol-
caniclastic unit in the southwestern part of Baja Cali-
fornia.

The Rosario embayment extends almost as far south
as the state line between Baja California and Baja Cal-
ifornia Sur and the boundary with the Vizcaino em-
bayment.

Fourteen marine terraces can be seen near Ensenada.
Ortlieb (1991) studied their ages, rates of uplift, and
correlation; uranium-series ages of corals and hydro-
corals from Punta Banda ranged from 80,000 to 1.3
Ma. Rockwell et al. (1989) and Muhs er al. (1992)
investigated rates of slip in the active Agua Blanca
Fault Zone, which delineates the northern boundary of
the Agua Blanca block.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 23

Tyuana A 32°N
r ( Rancho

Islas Ensenada

Todos ~S&

Town/village
Santos
fe)

y~Maneadero Mexico highway |
SS are Mesa Sepultura
Punta &Agua Banos 5 ae
Banda 5 wesenc need EZ, yoy Cantil Costero Fm
type area

D> Sones
Punta {aR ancho

China \__Alisitos

, As
10 Sango To eee,
7

\ San Vicente

Eréndira . ae

». San Rafael
San Antonio WY = ate
Od f ONL

® Rancho

Espinosa
eS rs
San Telmo

3] Nacional |

Cabo Pe

>N
~ Colonet >
eo
lary
im

~e
Camalu

a
io) ;
a Isla San Quintin
San Martin .
Ae \

J
\

Bahia de
San ae

Sierra San Pedro

fo]
So
=
=

50 KM

El Rosario

116° W aa epultura

Text-figure 5.—Rosario embayment, northern part, Ensenada to
El Rosario, B.C. Santillan and Barrera (1930) named the Alisitos
Formation for a section near Rancho Alisitos; they described the
Cantil Costero Formation from bluffs between Arroyo Hondo and
Arroyo Amarga.

Northern Rosario embayment, Ensenada to
Punta China
Plate 1, Column 4
(Text-figs. 2, 5, Table 3, Appendices 1, 2)

Column after Allison (1974) and Beggs (1984).
Area is shown on the Ensenada quadrangle, H11B12,
Rodolfo Sanchez Taboada quadrangle, H11B22, and
the Puerto San Isidro quadrangle, H11B32, scale 1:
50,000; and on the geologic maps of Gastil et al.
(1975) and Allison (1974).

Stratigraphy

Alisitos Formation, late Early Cretaceous.—Beggs
(1984) and Gastil et al. (1975), among others, discuss
the compiex history of relationships between the Ali-
sitos Formation and the Peninsular Ranges batholith.
Plutons were emplaced over a long time, some syn-
genetic with the Alisitos Formation and others pre-
dating or postdating it. Gastil et al. (1975: table 7)
included plutons dated at 90 and 130 Ma.

The Alisitos Formation is a sequence of volcanic

and marine volcaniclastic rocks and limestones that
was described from the Rio Santo Tomas valley south
of Ensenada. Allison (1974) mapped the type area and
reported on the unit’s lithologic diversity. He estimated
a greater thickness than in the original description,
7,500 m tor the formation as a whole, and listed a
large number of late Early Cretaceous age, Albian—
Aptian stage (120-99 Ma) megafossils. He recognized
two facies: a lower mudstone and an upper part con-
taining coarse andesitic breccia, tuffs, and interbedded
biohermal limestone with pachydont bivalves and cor-
als in living position.

Rosario Formation, Late Cretaceous.—The over-
lying Rosario Formation, named from a section in the
southern Rosario embayment, crops out extensively
for almost 500 km between the San Diego embayment
and Punta Canoas (Text-fig. 5). These are the Creta-
ceous rocks mentioned by White (1885) and Lindgren
(1888) that contain biostromes of the Upper Campa-
nian to Lower Maastrichtian Stage rudistid clam Co-
ralliachama orcutti White (Marincovich, 1975). Saul
(1970, figs. 1-26) illustrated a number of associated
shallow-water mollusks, including the gastropods Ho-
malopoma euryostoma (White), Nerita californiensis
White, and Benoistia pillingi (White), and the bivalves
Cymbophora sp. atf. C. ashburnerit (Gabb) and Calva
vartans (Gabb).

In the coastal areas the section is capped by Pleis-
tocene terrace deposits.

San Telmo Pluton, Cretaceous.—The San Telmo
Pluton was described from east of Mexico | in the
western foothills of the Sierra San Pedro Martir. Geo-
logic mapping and chronology studies of the granitoid
rocks by Delgado-Argote et al. (1995) near Rancho
Espinosa identified gabbro and diorite of approximate-
ly 100 Ma, quartz monzodiorite of 92 + 4 Ma and 82
+ 8 Ma; Bohnel and Delgado-Argote (2000) published
ages of 90 Ma to 100 Ma.

Mesa sandstone, obsolete name.—In 1867, W. M.
Gabb, the first geologist to traverse the entire Baja
California peninsula, used **... mesa sandstone, as I
shall call it for convenience” in field notes to describe
topography, not lithology. His narrative (Gabb, 1869a)
was part of J. Ross Browne’s official report on the
expedition, and focused on general physiography,
trails, and logistics. He did not name or describe any
formations, but discussed sizes and roundness of vol-
canic clasts. Most of the abundantly fossiliferous rocks
he saw contained oysters or internal molds that are not
readily differentiated from very worn Neogene and
Holocene specimens. In some instances the similarities
led him to estimate their ages as Pliocene.

24 BULLETIN 371

Ensenada =
a 0
“Jel Rasa"
-st, 0
\ Ro \
EI Rosario) \

Punta [<.|- O Mesa
Baja \ a la Sepultura +7

116° W

Bahia San
’> Luis Gonzaga
if zag
Catavifla \o~

J f
Punta Kk —\) Mesa
San Antonio = iV? San Carlos (

‘
ees ue :
Punta San Carlos ; » 5
=e d
\ A
Punta Canoas \\.__

Bat
: ?
en log rs de
29° N 2a > f — Nees
| 29° = \ | Punta ae
o ~~ Prieta
Cc Punta Maria~
N =
es \
2. LSA Rosarito
ao
Lomas las
Tetas de Cabra
0 SOKM 7

ee ees

(\Isla ~~
a ) Cedros So

vA / \ if ao Cq
va en ¢/Cedros ION
- was S| 28°N
| Punta SOS “4 At{—-—
116° W . Eugenia Punta de GLE er
Isla VQ Malarrimo Guerrero
Natividad \ TS (Negro
e §=Town/village . 2 \\ Bahia Tortugas ~ »

@ Mexico highway | 115° w 114° W

Text-figure 6.—Southern Rosario embayment, map showing E
Rosario to 28° N, including Mesa la Sepultura, Mesa San Carlos,

Punta Maria, and Lomas las Tetas de Cabra

The mesa-forming sediments Gabb observed be-
tween La Paz and Ensenada are now referred to a num-
ber of different units, both Mesozoic and Cenozoic,
sedimentary and igneous. Early workers, including
Lindgren (1888, 1889, 1890), Emmons and Merrill
(1894), and Willis and Stése (1912), attached the name
to Cretaceous rocks in the Ensenada area; Darton
(1921) used it for rocks overlying the “Yellow beds”
in Arroyo la Purisima, but did not call it a formation.
Heim (1922: 530) pointed out that the “so-called Mesa
sandstone” of the northern peninsula is Late Creta-
ceous and lithologically different from the Tertiary age
“Mesa Sandstone” of the southern peninsula. As such,
he concluded, the name could not be applied to a
stratigraphic unit; it was neither a useful nor a valid
term.

Southern Rosario embayment
Plate 1, Columns 5, 6
(Text-figs. 2, 6, Table 3, Appendices 1, 2)

The main part of the southern Rosario embayment
extends from north of the town of El Rosario to Punta
Canoas, north of the Baja California/Baja California

Sur state line (Text-fig. 6). It is underlain by Late Cre-
taceous to Paleocene deep marine to nonmarine sedi-
ments that have undergone tectonic subsidence and up-
lift, folding, faulting, and tilting. Busby er al. (1998)
reviewed the stratigraphic units within the tectonic and
depositional settings of the Peninsular Ranges fore-are
basin. Sections at Mesa la Sepultura and Mesa San
Carlos were sampled for evidence of the K/T boundary
(Abbott er al/., 1993b), but it was not found in either
sequence. Geologic maps and stratigraphic summaries
of selected areas are included guidebook articles such
as W. R. Morris and Busby (1996).

San Quintin to El Rosario, Baja California
Plate 1, Column 5

(Text-figs. 1, 2, 5, Table 3, Appendices 1, 2)

Column for San Quintin is from Santillan and Ba-
rrera (1930). Area shown on the Venustiano Carranza
quadrangle, H!1B74, and El Rosario quadrangle,
H11B84, scale 1:50,000; and on the geologic map of
Gast et al. (1975), scale 1:250,000.

Overview

The San Quintin area, 190 km (119 m1) south of
Ensenada, is known for the Quaternary San Quintin
Volcanic Field. Luhr ef al. (1995) studied the basalts,
which were dated at 0.73—0.22 Ma by Aranda-Gomez
et al. (1993). Basement rocks are overlain by the late
Early Cretaceous Alisitos Formation to the east and by
the Late Cretaceous Rosario Formation. A thin Plio-
cene marine unit caps the section south of San Quintin.

Stratigraphy

Rosario Formation, Late Cretaceous.—The Rosario
Formation includes sandstones, siltstones, shales, and
conglomerates that contain abundant Late Cretaceous
fossils (Table 3). It crops out west of the Peninsular
Ranges batholith.

Cantil Costero Formation, Late Pliocene.—The
Cantil Costero Formation extends along the east side
of Mexico 1, from Bahia San Quintin to Punta Baja
(Johnson and Ledesma-Vazquez, 1993; Ledesma-Vaz-
quez and Johnson, 1994). The type section is a poorly-
sorted transgressive marine conglomerate that contains
Late Pliocene fossils such as Pecten (Pecten) bellus
(Conrad), Acanthina emersoni Hertlein and Allison,
and clusters of the large barnacle Balanus gregarius
(Conrad). The barnacle is also Known from the latest
Pliocene or earliest Pleistocene upper member of the
San Diego Formation and from Pliocene strata of the
Almejas Formation of the Vizcaino peninsula (J.T.
Smith, 1984). An abrasion platform developed on the
underlying Rosario Formation is extensively bored by

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

the Holocene pholad clam Penitella penita (Conrad)
in concentrations of 200 individuals per square meter
(Ledesma-Vazquez and Johnson, 1993).

El Rosario to Mesa la Sepultura, Mesa San Carlos,
and Rosarito
Plate 1, Columns 6 and 7
(Text-figs. 2, 5, 6, Table 3, Appendices 1, 2)

Columns after Abbott ef al. (1993a,b), Abbott er al.
(1995), W. R. Morris and Busby (1996), Busby er al.
(1998), and D. P. Smith (written communication,
1998). Area is shown on El Aguajito quadrangle,
H11B85, Emiliano Zapata quadrangle, HI1D15, Ro-
sarito quadrangle, H11D69, 1:50,000, and on the geo-
logic maps of Gastil ef al. (1975); Kilmer (1963), Ren-
ne et al. (1991), and W. R. Morris and Busby (1996).

Stratigraphy
Units exposed in this part of the Rosario embayment
are Cretaceous to Paleocene marine and nonmarine
fore-arc basin deposits that overlie Late Jurassic to
Late Cretaceous Peninsular Ranges plutons. Ages are
from D. P. Smith (written communication, 1998).

Informal units of Kilmer (1963), Late Cretaceous.—
Kilmer (1963) gave informal names to three Late Cre-
taceous sedimentary units in the area south of El Ro-
sario and northeast of Punta Baja. Although he did not
publish formal descriptions, the names have been used
informally in subsequent literature, especially field
guidebooks. The formations and members are not
shown individually in Plate 1, Columns 6 and 7, be-
cause they represent a relatively short time, 73—78 Ma
(L. R. Saul, written communication, 2003). Their out-
crop areas were mapped by W. R. Morris and Busby
(1996: fig. 4).

Brief descriptions and type section locations are giv-
en in Table 3 for the following:

“La Bocana Roja formation,” Late Cretaceous.—

“Punta Baja formation,” Late Cretaceous.—

“El Gallo formation,” Late Cretaceous, and its three
members: “La Escarpa,” “El Disecado,” and “El
Castillo.”

Rosario Formation, Late Cretaceous.—The Upper
Campanian to Lower Maastrichtian Stage Rosario For-
mation overlies the preceding units. In this area it is
divided into lower near shore deposits and an upper
deep marine sequence (W. R. Morris and Busby, 1996;
Busby er al., 1998). A paleosol separates the top of
the Rosario Formation from the overlying Sepultura
Formation on the northeast side of Mesa de la Sepul-
tura; a disconformity marks the contact at Mesa San
Carlos, 40 km to the south. Faunal stage determina-
tions are from Durham and Allison (1960).

bo
Nn

Sepultura Formation, Paleocene.—Late Early to
early Late Paleocene fan delta to submarine fan de-
posits of the Sepultura Formation crop out discontin-
uously between the towns of El Rosario and Puerto de
San Carlos. Lesdesma-Vazquez (1991) studied the
lower glauconitic member, which contains storm de-
posits and shallow-marine facies at its base that grade
upward to shelf deposits of 200 m depths. Sampling
at Mesa de la Sepultura to identify the K/T boundary
within the unit indicated that the basal sediments con-
tain abundant younger, Late Paleocene microfossils
(Abbott ef al/., 1993) and Upper Thanetian Stage mol-
lusks such as Turritella peninsularis Anderson and
Hanna (Squires et al., 1989; Abbott et al., 1995) and
Popenoeum maritimus Squires, Zinsmeister, and Pa-
redes-Meyjtia.

Zinsmeister and Paredes-Mejia (1988) reported con-
siderable taxonomic diversity in the mollusks from
Mesa San Carlos, **... comparable to coeval tropical
faunas of the Gulf [of Mexico] Coast Paleocene.”
They noted exceptional preservation of shells, some
with color patterns, and warmer water assemblages
than in penecontemporaneous basins in southern Cal-
ifornia.

Correlation of the Sepultura Formation.—Fife
(1968) mapped limestone outcrops at Punta Marta
(29°00' N, 114°30' W) that Abbott ef al. (1995) infor-
mally named the Punta Marta limestone member of
the Sepultura Formation. They described the unit as a
red-algal biosparrudite containing benthic foramini-
fers; interfingering sandstone facies bear abundant Ve-
nericardia and the early Late Paleocene index species
Turritella peninsularis Anderson and Hanna. The Pun-
ta Maria limestone member correlates with the Los
Cuervitos limestone member of the Bahia Ballenas
Formation of the Vizcaino embayment (D. P. Smith i
Abbott er al., 1995) and the Sierra Blanca Limestone
of southern California.

Lomas Las Tetas de Cabra Formation, Eocene.—I\n
the badlands 30 km south of Punta Prieta the Sepultura
Formation interfingers with or grades upward to the
continental Lomas Las Tetas de Cabra Formation. No-
vacek et al. (1991) described the sediments and Early
Eocene vertebrates from a locality known also as Oc-
cidental Buttes (Gastil ef al/., 1975).

Vizcaino embayment
Plate 1, Columns 8, 9, 10, 11, 12
(Text-figs. 1, 2, 7, 10, Table 4, Appendices 1, 2)
Overview
The Vizcaino embayment stretches almost 200 km
from Isla Cedros across the Vizcaino peninsula to Pun-
ta Abreojos, west of Laguna San Ignacio. It is under-

BULLETIN 371

Table 3.—Rosario embayment, lithostratigraphic units. Ensenada to Mesa San Carlos, Baja California, including Punta China, El Rosario,

and Mesa de la Sepultura (Text-figs. 5, 6). Lowercase names indicate informal units that were not established according to the North American

Stratigraphic Code (1983).

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Alisitos Formation

Cantil Costero Forma-
tion

“El Castillo member,”
informal name

“El Disecado mem-
ber,” informal name

“El Gallo formation,”
informal name

“La Bocana Roja for-
mation,” informal
name

“La Escarpa member,”

informal name

Santillan and Barrera (1930)
named; Allison (1974) ampli-
fied original description, rec-
ognized two members. Beggs
(1984) raised to Group, identi-
fied seven volcanic and vol-
caniclastic facies A—G.

Santillan and Barrera (1930).

Kilmer (1963) named as member
of “El Gallo formation.”

Kilmer (1963), also named three
informal members: “El Castil-
lo,” “El Disecado,” and “‘La
Escarpa.””

Kilmer (1963)

Kilmer (1963) included in “El
Gallo formation.”

Formation is a lithologically diverse, metavolcanic, and metasedimen-
tary unit described from Rancho Alisitos and Arroyo la Cueva, Ro-
dolfo Sanchez Taboada quadrangle. Clastic sediments are finer in
the lower part of the section, coarser in the upper part between
Punta China and Los Muertos, Puerto San Isidro quadrangle, where
they occur with tuffs and interbedded rudistid limestones. Beggs
(1984) classified the volcanic facies, their environments of deposi-
tion and distributions. Late Early Cretaceous (119—97.5 Ma), Albi-
an—Aptian Stage, based on megafossils (Allison, 1974).

Formation is a thin, flat-lying marine fossiliferous conglomerate with
a sandstone matrix that caps the mesas south of San Quintin, Ven-
ustiano Carranza quadrangle. Type section is south of San Quintin
and east of Mexico 1, 14-20 km north El Rosario. An abrasion
platform developed on the disconformity exposed between Arroyo
Hondo, km 35, and Arroyo Amargo, km 41 (Ledesma-Vazquez and
Johnson, 1994). Late Pliocene.

Member consists of fluvial to shallow marine sediments that crop out
discontinuously in the eastern part of the Rosario embayment. They
interfinger with the “El Disecado member” north of El Rosario
and east of Punta Canoas. Late Cretaceous.

Unit is a sequence up to 1,000 m thick of interbedded fluvial to tidal
mudstones, sandstones, and minor tuffs (W. R. Morris and Busby,
1996). Exposed north and south of Rio del Rosario in both eastern
and western margins of the Rosario embayment, it also crops out at
Punta San Antonio. The member contains a basal bentonite dated at
74.25 + 0.07 Ma and an altered tuff higher in the section with K-
Ar ages of 73.59 + 0.9 Ma and 73 + 2 Ma, respectively (Renne er
al., 1991; G. B. Dalrymple in W. J. Morris, 1981). Most of the ver-
tebrates collected from the “El Gallo formation” came from this
member and the interval between the dated samples. Late Creta-
ceous age, Upper Campanian Stage.

Unit is a mainly nonmarine sequence of fluvial to tidal conglomer-
ates, sandstones and tuffs more than 1,246 m thick (W. R. Morris
and Busby, 1996). Its members crop out discontinuously in the
eastern and western parts of the Rosario embayment, mostly (ex-
cept for the “El Disecado”” member) south of Rio del Rosario, in
the El Rosario and Punta Baja quadrangles. “El Gallo formation”
overlies the “Punta Baja formation” and is overlain with angular
unconformity by the Rosario Formation. It contains fossil verte-
brates, including dinosaurs (bones, also casts of scales or skin),
mammals and birds (W. J. Morris, 1974a; 1981). Late Cretaceous
age, Upper Campanian Stage.

Oldest of Kilmer’s Late Cretaceous units, the formation consists of
more than 1,260 m of gently unfossiliferous folded fluvial sand-
stones, siltstones, claystones, and conglomerates (W. R. Morris and
Busby, 1996). Nominal type section is exposed along the coast east
of Punta Baja in the quadrangle of the same name. Unit is uncon-
formably overlain by the “Punta Baja’ and “El Gallo” formations.
Early Late Cretaceous (W. R. Morris and Busby, 1996).

Unit consists of 800 m of coarse-grained alluvial fan and braided
stream deposits (Renne et a/., 1991) that crop out discontinuously
south of Rio del Rosario as far as Punta San Antonio, El Rosario
and Punta Baja quadrangles. Unconformably overlain by the “El
Disecado”” member. Late Cretaceous age, Campanian Stage, brack-
eted by #Ar/Ar dates of 74.87 + 0.05 Ma for a basal bentonite
and 74.46 + 0.08 Ma for a tuff higher in the section (Renne er al.,
1991).

Table 3.—Continued.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 27

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Lomas las Tetas de Ca-

Novacek er al. (1991).

bra Formation

“Punta Baja forma- Kilmer (1963).
tion”, informal

name

Abbott ef al. (1995) named; Fite
(1968) mapped as Sepultura

Punta Maria limestone
member, informal
name Formation.

Santillan and Barrera (1930)
named; Anonymous (1924)
mentioned (Table 2).

Rosario Formation

San Telmo Pluton Woodford and Hariss (1938).

Santillan and Barrera (1930)
named; Abbott er al. (1993)
distinguished two members.

Sepultura Formation

Formation is a red and brown sandstone and siltstone described from
an area known as Occidental Buttes or Las Tetas de Cabra, I—1.5
km west of Mexico | and approximately 7 km northwest of Rosari-
to, in the quadrangle of the same name. Overlain by unnamed
coarse-grained sandstone and conglomerate. Early Eocene, Was-
atchian Land Mammal Stage, based on vertebrates (Novacek ef al.,
1991), 57-51 Ma.

Unit is a series of gently undulating deep-marine conglomerates,

sandstones, shales, and siltstones described from approximately one
mile north of Punta Baja. W. R. Morris and Busby (1996) regarded
them as bathyal submarine canyon deposits that overlie the “La
Bocana Roja formation” in the western Punta Baja quadrangle.
Unit is unconformably overlain by the “‘La Escarpa member” of
the “El Gallo formation.” Late Cretaceous age, lower Upper Cam-
panian Stage, 77-74 Ma (based on an ammonite, fide L. R. Saul,
written communication, 2003).

Unit is a fossiliferous sandy red-algal biosparrudite and limestone

with sandstone interbeds described at Punta Maria, Punta El Diablo
quadrangle. It is regarded as the upper member of the Sepultura
Formation and correlated with the Los Cuervitos limestone member
of the Bahia Ballenas Formation in the southern Vizcaino embay-
ment (D. P. Smith in Abbott ef al., 1995). Late Paleocene.

Formation was described as a sequence of sandstones, shales, and

conglomerates with abundant marine invertebrates. Type section Is
near the town of El Rosario in the quadrangle of the same name. It
is unconformable above the Alisitos Formation, unconformably
overlain by the Sepultura Formation. Late Early Cretaceous, no
younger than Middle Maastrichtian Stage (L. R. Saul, written com-
munication, 2003).

Unit consists of multiple plutons described from the western foothills

of the Sierra San Pedro Martir, south of Arroyo San Rafael near
Rancho Espinosa and San Telmo, Punta Colnet quadrangle. Em-
placement could have occurred over a 20 m.y. period (Delgado-Ar-
gote ef al., 1995). Late Early Cretaceous.

yrmation is a marine sandstone alternating with conglomerates and
limestones described from Mesa de la Sepultura (30°00! N, 115°30'
W) approximately 20 km east-southeast of El Rosario, E] Aguajito

quadrangle. Abbott et a/. (1993) recognized a lower megafossilifer-
ous glauconitic-clastic member with red-algal rhodolith nodules and
an upper deep-water limestone bearing foraminifers and red algae.
Late Early to early Late Paleocene age at Mesa la Sepultura. Teél-
lez-Duarte and Helenes (2002) noted a finer facies and absence of
carbonates in the unit at Mesa San Carlos, where it is also Late

Paleocene.

lain by rocks of Triassic to Pliocene age. It differs from
the rest of western Baja California Sur in its tectonos-
tratographic history and in the great thickness, more
than 8 km, of its exposed sedimentary section (Boles,
1986; D. P. Smith ef al., 1993a,b).

The Vizcaino peninsula lies west of the Peninsular
Ranges and east of the offshore Tosco-Abreojos and
San Benito Fault Zones. Coney er al. (1980) regarded
it as the Vizcaino terrane. Shallow magnetic inclina-
tions reported in several Cretaceous units in the Viz-
caino embayment suggest 15° of post mid-Cretaceous
northward translation with respect to North America

(Filmer and Kirschvink, 1989; D. P. Smith and Busby,
1993), but workers continue to explore alternative in-
terpretations to explain the data. Sedlock (1993, 2000)
summarized later interpretations that recognize upper
and lower convergent margin plates separated by an
ophiolite. The upper plate consists of three different
oceanic terranes: Choyal, Vizcaino Norte and Vizcaino
Sur.

Unlike the Tertiary marine embayments to the north
and south, the Vizcaino embayment underwent an
abrupt deepening to middle bathyal depths in the late
Early Miocene, as documented by stratigraphic and pa-

28 BULLETIN 371

leontologic studies of the Tortugas Formation north of
the town of Bahra Tortugas (Helenes and Ingle, 1979;
Helenes-Escamilla, 1980).

The stratigraphic units of the Vizcaino embayment
include a number of time-transgressive formations,
many of which were revised as new mapping was
completed. Bottjer and Link (1984), Boehlke and Ab-
bott (1986) and Busby-Spera (1988), among others,

discussed these changes.

Basement Rocks of the Vizcatno embayment.—
Metamorphic basement rocks, including a serpentinite-
matrix mélange with blocks of blueschist and greens-
chist, lie in fault contact with ophiolites and volcanic
arc-related units (Rangin, 1979; T. E. Moore, 1985,
1986; Kimbrough, 1985; Sedlock, 1988, 1993). Sed-
lock (1993) summarized the structural units of the Viz-
caino embayment and the islands of the western Mag-
dalena Plain 400 km to the south, as follows: an upper
plate (Triassic and Jurassic are and ophiolitic rocks
overlain by Cretaceous turbidites), lower plate (blues-
chist metamorphic rocks, including red ribbon radio-
larian chert), and an intervening fault zone containing
serpentinite-matrix mélange consisting of exotic
blocks of amphibolite, blueschist, eclogite, greenschist,
and ultramafic rocks. This complex is also known as
the Puerto Nuevo area mélange complex of T. E.
Moore (1986) and the Sierra Placeres mélange of Sed-
lock (1993).

Stratigraphic Summary

Mina-Uhink (1957) mapped the area and named
many of the earliest recognized units, which were sub-
divided and mapped by a number of graduate students
and professors from the 1970s to the present. This
work is summarized in the guidebooks of Abbott and
Gastil (1979) and Frizzell (1984) and the papers of D.
P. Smith er al. (1993a,b), and Abbott er al. (1995).
Some of the new units lack formal type section des-
ignations, having been analyzed and discussed in un-
published theses and guidebooks. These are regarded
as informal units in Table 4, which lists names, au-
thors, and type areas for the principal formations and
members in the area.

D. P. Smith ef al. (1993a) used data from mapping
and basin analyses to refine stratigraphic units of vary-
ing rank. They raised the Valle Formation of Mina-
Uhink (1957) to a Group and included seven lithologic
units as formations within it. Ongoing studies by D. P.
Smith, D. L. Kimbrough, T. E. Moore, and others con-
tinue to refine the formal stratigraphy of the Valle
Group. D. P. Smith, C. Busby, and other workers focus
on the relation of Mesozoic units to convergent margin
settings and progressive tectonic phases, from exten-

38° 29''N 115° 29'N _~) Punta Norte

e Town/village
WS Late Miocene-
Early Pliocene |
Almejas Formation J

late Early Miocene- ff Isla
early Late Miocene ( Cedros
Tortugas Formation ’
Fault IN
S
v
N
Arroyo
Coloradito

Arroyo
San Carlos

Cedros

Cabo San
Augustin

( Punta Morro

ey Redondo | .

Punta Prieta~ ‘
115°}20"N___03'N
Text-figure 7.—Isla Cedros, B.C.S., map showing Neogene ma-
rine outcrops and general geology modified from Kilmer (1984).
Kilmer (1984) mapped a narrow band of Almejas Formation along
the east coast for 8-10 km north and | km south of the Arroyo
Choyal Fault, and a 20-m-thick white sandstone facies of the Tor-
tugas Formation at the southern end. South of the town of Cedros,
Rangin (1979) and Kilmer (1984) mapped 1.5 km of northwest-
dipping marine sediments that include the Tortugas Formation and
the Almejas Formation vertebrate locality of L. G. Barnes (1992)
and L. G. Barnes et al. (1997).

sional to compressional systems. They recognize an
early subduction stage at 200-130 Ma and a later one
at 140-100 Ma.

Isla Cedros, northern Vizcaino embayment
Plate 1, Column 8
(Text-figs. 2, 7-10, Table 4, Appendices 1, 2)

Column after D. P. Smith and Busby (1993b) and
D. P. Smith (written communication, 2000). Geologic
maps include those by D. P. Smith er al. (1993b), D.
P Smith and Busby (1993b), Sedlock (1988, 1993),
and Kilmer (1977, 1984).

Stratigraphy

Mesozoic basement rocks.—The basement of Isla
Cedros includes a Jurassic island-are complex in the
north and a Jurassic ophiolite assemblage south of Ar-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 29

royo Choyal (Kimbrough, 1985). These rocks are
structurally underlain by Jurassic to Cretaceous blue-
schist grade metamorphic rocks of the western Baja
Terrane (Kimbrough, 1985; Sedlock, 1988). Kim-
brough (1984), Busby-Spera (1988), and Boles and
Landis (1984) studied the sedimentary sequences and
summarized, after Kilmer (1977), the lower units that
crop out on the island: the Cedros mélange and a Mid-
dle to Late Jurassic ophiolite (Kimbrough 1982, 1984),
the overlying Gran Canon formation and Coloradito
formation (informal names), Eugenia Formation, and
a large section referred to the Valle Group. D. P. Smith
et al. (1993b) distinguished the Late Cretaceous Var-
gas Formation and the overlying Late Cretaceous Pi-
nos Formation as units within the Valle Group in the
central and southern parts of Isla Cedros. The lower
parts of the Vargas Formation correlate with the Los
Chapunes formation, informal name, of the Vizcaino
peninsula.

Tortugas Formation and Almejas Formation of Isla
Cedros, Miocene and Pliocene.—Tertiary marine
rocks referred to the Tortugas and Almejas Forma-
tions, both described from the Vizcaino Peninsula by
Mina-Uhink (1957), crop out south of the town of Ce-
dros and north of Gran Canon on the east side of the
island (Text-fig. 7). The Late Miocene to Early Plio-
cene Almejas Formation contains a rich diversity of
vertebrates and invertebrates at a locality south of the
town of Cedros that has yielded one of the most im-
portant sections for vertebrate taxa from this time pe-
riod in the North Pacific (L. G. Barnes, 1973, 1984,
1992; Aranda-Manteca and Barnes, 1993). Just north
of Gran Canon and south of Arroyo Choyal, approx-
imately 15 km north of the town, the Almejas For-
mation consists of unsorted megafossiliferous con-
glomerates that contain reworked Miocene mollusks
(J. T. Smith, 1984, 1991a; Kilmer, 1984; Text-figs. 8,
9 herein). Hanna (1927) estimated the thickness of ex-
posed marine Pliocene rocks on the island as 30 m
(less than 100 ft).

Northern Vizcaino peninsula,
Punta Eugenia to Bahia Tortugas
Plate 1, Columns 9, 10
(Text-figs. 1, 2, 10-12, Table 4, Appendices 1, 2)

Columns after Helenes-Escamilla (1980, 1984), He-
lenes (1984), and D. P. Smith (written communication,
1998). Area is in the Punta Eugenia quadrangle,
G11BI17, and the Bahia Tortugas quadrangle, G1 1B27,
1:50,000. The geology was mapped by Robinson
(1975), Rangin (1979), Helenes-Escamilla (1980),
Hickey (1984), and Patterson (1984).

Overview

The northern part of the Vizcaino peninsula mapped
by Robinson (1975, 1979a) includes the type section
of the Eugenia Formation, which is separated by faults
from adjacent units. Age and lithology vary between
structural blocks, from latest Jurassic or Early Creta-
ceous in the west to Middle Cretaceous in the east
(Boles and Hickey, 1979).

The late Early Cretaceous Valle Formation was first
mapped and named by Mina-Uhink (1957) in the area
of Valle Salitral, east and southeast of Bahia Tortugas
(Text-fig. 10). Because the focus of this paper is Ter-
tiary stratigraphy, we briefly mention the units that
Were mapped in the Valle Group, some of which are
in contact with Tertiary marine formations (Table 4).
Berry and Miller (1984) reported on Jurassic and Cre-
taceous foraminifers, radiolarians, and calcareous nan-
noplankton as part of the University of California,
Santa Barbara’s Vizcaino Project of the late 1970s and
1980s.

Sedimentology and microfossils reflect a three-stage
evolution of the Vizcaino embayment, beginning in the
Early Miocene with rapid subsidence from subaerial
to middle bathyal depths. A Middle Miocene uplifting
event triggered deposition of turbidites in the deeper
part of the basin, followed by Late Miocene subsi-
dence (Helenes-Escamilla, 1980). Such extreme depth
changes are not seen in penecontemporaneous embay-
ments elsewhere in western Baja California.

Pleistocene terrace deposits of the Vizcaino Penin-
sula were studied by Emerson er al. (1981) and Ortlieb
(1979,, 1991),

Stratigraphy

Mesozoic sediments, latest Jurassic to Early Cre-
taceous.—Latest Jurassic—Early Cretaceous metamor-
phic rocks crop out southeast of Punta Eugenia and
west of a group of faults referred to the Playa Negra
fault zone (Boles and Hickey, 1979)

In the northern Vizcaino Peninsula Cretaceous sed-
iments were referred to the Eugenia Formation, the
informally named Perforada formation of Hickey
(1984), the Los Chapunes formation of Patterson
(1984), and the undivided Valle Formation, which was
regarded as the Valle Group by D. P. Smith er al.
(1993a). These units are overlain with angular uncon-
formity by the Miocene Tortugas Formation: the con-
tact between the Valle Formation and the Tortugas For-
mation is well exposed approximately 1.5 km north-
east of the Bahia Tortugas harbor (Text-fig. 10).

Tortugas Formation, late Early to early Late Mio-
cene.—Helenes-Escamilla (1980) divided the type sec-
tion of the Tortugas Formation northeast of the town

30 BULLETIN 371

bald
115° W

BAJA
Punta CALIF.

BAJA CALIF. SUR

Quebrada
Bahia San Jose _
Tortugas ~~ de Castro----7" BA
Pusito y* -- Cerro del Elefante San
1 rain er > macl
Nuevo za Mesa de Ignacio

ae) Wa
ve aS
\

las Auras
Punta San Roque
Bahia \ Sierra de’

Asuncion Santa Clara
: :

Punta Abreojos
Laguna
San Ignacio

Mexico highway |

Unpaved road

Town/village

K/Ar age locality (Sawlan and Smith, 1984)
Rancho

Type section

LSS WwW.

Text-figure 8.—Arroyo Choyal, northeastern Isla Cedros, area of California Academy of Sciences locality 946 collected by Hanna and
Jordan in 1925, Late Miocene, Almejas Formation. Photo, J. T. Smith, 1979.

Text-figure 9.—Arroyo Choyal, outcrop in small canyon to the south with unsorted conglomerates containing disarticulated valves of the
Late Miocene pectinid Lyropecten gallegosi (Jordan and Hertlein). Photo, J. T. Smith, 1979.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 31

of Bahia Tortugas into two members, A and B, and
the section at Punta Quebrada, 10 km to the northwest,
into four members, 1—4. He conducted a quantitative
analysis of foraminifers, diatoms, and sediments to de-
termine paleoenvironments and basin history, and re-
lated local faunal zones to the West Coast benthonic
foraminiferal stages of Kleinpell (1938, 1980).

Member A of the type section contains yellow-gray
sandstone that weathers to brown and phosphorite with
silicified shells of late Early to early Middle Miocene
mollusks. Molluscan index species include Aequipec-
ten discus (Conrad), Lucinoma sp. ct. L. sanctaecrucis
(Arnold), and Turritella ocoyana Conrad (J.T. Smith,
1984). It is a shallower water correlative of Members
| and 2 that represent Early to Middle Miocene bathy-
al conditions at Punta Quebrada. Member B at the air-
field consists of diatomaceous shales with microfossils
that indicate an environment similar to that of Mem-
bers 3 and 4 at Punta Quebrada (Helenes-Escamilla,
1980). McGee (1967) also reported diatomite in the
Tortugas Formation from Isla Cedros (Text-fig. 7).

At the type section, Helenes-Escamilla (1980) re-
ferred the lower part of Member A to the Relizian—
Luisian Stage, lower Middle Miocene age (15.5—13
Ma) Cibicides floridanus local zone. Overlying Mem-
ber B represents the lower Mohnian Stage, Middle
Miocene age (13—9.8 Ma) Bulimina uvigerinaformis
zone.

At Punta Quebrada the basal section ranges from
the upper Saucesian Stage, late Early Miocene to early
Middle Miocene Rectouvigerina mayi Zone (Member
1) to the upper Mohnian Stage, Early Miocene age
Bolivina girardensis Zone (Member 4). Intermediate
member 2 contains the Relizian to lower Mohnian
stages. Middle Miocene age Cibicides floridanus and
lower Bulimina uvigerinaformis zones. Member 3 has
lower Mohnian Bulimina uvigerinaformis Zone fora-
minifers and abundant diatoms of the late Middle to
early Late Miocene Denticula hustedtii/D. lauta Zone
(13.5—9 Ma).

Correlation

White calcareous sandstone and siltstone near San
Ignacio could correlate with the Tortugas Formation,
which crops out discontinuously between Punta Que-
brada and the town of Asuncion. Agatized megatossils
from a quarry near Microondas Abulon (km 88 on
Mexico | and 4.7 km west of the turnoff to San Ig-
nacio; Text-fig. 10) include some of the same taxa as
in Member A of the Tortugas Formation.

The Tortugas Formation correlates with the Rosarito
Beach Formation, Los Indios Member, of the La Mi-
sion area, Baja California. Its megafaunal composition
is closer to that of the southern California embayments
than to the penecontemporaneous Salada Formation of
the Magdalena Plain, 250 km to the south.

Almejas Formation, Late Miocene to Early Plio-
cene.—Outcrops of the Almejas Formation vary in age
from Late Miocene to Early Pliocene, determined by
abundant megafossils and constrained by overlying ba-
salts of 6.48 + 0.23 Ma and 5.7 + 0.2 Ma (J. T. Smith,
1984). Fossil mollusks, barnacles and echinoids col-
lected from a monadnock 3 km south of town (Text-
fig. 12) suggest shallow neritic depths similar to the
present Bahia de Almejas. Miocene taxa include Fo-
rreria wrighti Jordan and Hertlein, Trophon sp. ct. Fo-
rreria belcheri (Hinds) of Durham and Addicott, and
Leptopecten praevalidus (Jordan and Hertlein). Rep-
resentative Pliocene mollusks include Litusyapecten di-
lleri (Dall), Pecten (Pecten) bellus (Conrad), Argopec-
ten percarus (Hertlein), and *‘Ostrea” veatchii Gabb
(J. T. Smith, 1984); these species and others are also
found in the lower part of the San Diego Formation.

Southern Vizcaino embayment,
San Roque—Asuncion—San Hipolito—
Punta Abreojos
Plate 1, Columns 11, 12
(Text-figs. 2, 10, Table 4, Appendices 1, 2)
San Roque and San Hipolito columns after D. P.
Smith (written communication, 1998), Whalen and

<—

Text-figure 10.—Vizcaino embayment, map of Isla Cedros to Laguna San Ignacio, B.C.S. Open circles indicate type sections: 1, Valle
Formation; 2, Tortugas Formation; 3, Almejas Formation, 4, San Ignacio Formation. K/Ar ages for basalts capping Cerro del Elefante and
Mesa de las Auras are 6.48 + 0.23 Ma and 5.70 + 0.20 Ma, respectively (Sawlan and J. G. Smith, 1984). Basalt of Rancho Esperanza has a
K/Ar age of 9.72 + 0.29 Ma west of San Ignacio at the turnoff to San Lino (km 74) (Sawlan and J. G. Smith, 1984). Quarry along Mexico
1 west of Microondas Abulon (km 88) contains agatized Turritella sp. and other mollusks also found in the Tortugas Formation. Beal (1948)
reported that Marland Oil Company reconnaissance geologists collected extensively near Rancho San Angel, which has abundant identifiable
fossils represented by internal molds; the specimens are now at the California Academy of Sciences, San Francisco. PM, Punta Malarrimo.

Text-figure 11.—Martin Lagoe standing on the angular unconformity between brown turbidite sands of the Cretaceous Valle Formation and
light-colored pelletal phosphorite and sand facies of the Miocene Tortugas Formation. Area is 1.5 km northeast of the harbor in the town of
Bahia Tortugas. Photo, J. C. Ingle, Jr, 1980.

— oS

Text-figure 12.—Monadnock of highly fossiliferous Late Miocene Almejas Formation sandstones, 3 km southeast of Bahia Tortugas. This
is California Academy of Sciences locality CAS 945 collected by Hanna and Jordan in 1925. Photo, J. T. Smith, 1982,

ws)
bo

BULLETIN 371

Table 4.—Vizcaino embayment, Baja Californa Sur, lithostratigraphic units (Text-figs. 7, 10). Lowercase names indicate informal units that
were not established according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Almejas Formation

Asuncion formation,
informal name

Bahia Ballenas Forma-
tion

Bateque Formation
(used by some au-
thors in the Vizcaino
embayment)

Cedros ophiolite, infor-
mal name

Choyal formation, in-

formal name

Coloradito formation,
informal name

Conglomerados los
Juncos, informal
name

Eugenia Formation

Mina-Uhink (1957).

D. A. Barnes (1982, 1984); D. P.
Smith et al. (1993) included in
the Valle Group.

New name of Abbott er ai.
(1995) for the informally
named ~Ballenas formation”
of Sorensen (1982); D. P.
Smith er al. (1993b) included
in the Valle Group.

Mina-Uhink (1957) named and
mapped east of Laguna San
Ignacio. Sorensen (1982) used
“Ballenas formation” for out-
crops in the Vizcaino peninsu-
la; D. P. Smith in Abbott er al.
(1995) proposed a new name
for these rocks.

Kilmer (1963, 1977, 1979): also
discussed by Kimbrough
(1984, 1985) and Sedlock
(1993):

Kilmer (1977, 1979); Kimbrough
(1984); Sedlock (1993).

Kilmer (1977, 1979); Boles and
Landis (1984) and Kimbrough
(1984) also discussed.

Drake (1995). D. P. Smith er al.
(1993b) regarded as a forma-
uon in the Valle Group.

Mina-Uhink (1957) named. Boles
and Landis (1984) and Sed-
lock (1993) also discussed.

Formation consists of fossiliferous sandstone, shale, and conglomerate
facies: the contact with the underlying Tortugas Formation has not
been observed. Type section is in Arroyo Bateque, 15 km southeast
of the town of Bahia Tortugas, Bahia Tortugas quadrangle, North of
Asuncion the Almejas Formation is capped at Cerro del Elefante
and Mesa de las Auras by basalts of 6.48 + 0.23 Ma and 5.7 +
0.2 Ma, respectively (J. T. Smith, 1984, 1991¢). Late Miocene to
Early Pliocene, based on fossils and associated volcanic rocks (J. T.
Smith, 1984).

Unit consists of 800-900 m of coarse-grained tuffaceous and calcar-
enaceous rocks, reworked carbonate debris, and matrix-supported
conglomerate in the southern Vizcaino peninsula. Chaotic basal
sediments contain enormous clasts 25—150 m in diameter; the lime-
stones have large orbitolinid foraminifers. Type section is approxi-
mately 17 km north-northwest of Asuncion, near Rancho San An-
drés on the south side of Cerro del Elefante, Puerto Nuevo
quadrangle. Late Early Cretaceous, Aptian-Albian Stage, based on
radiolarians and calcareous nannofossils (D. A. Barnes, 1984).

yrmation is a 2-km-thick bathyal siliciclastic shale that includes a
basal breccia, the Los Cuervitos limestone with transported shal-
low-water marine fossils, and five shell bed layers. Type section is
near Rancho el Carrizo, 40 km north of Punta Abreojos, Punta
Abreojos quadrangle. Early Paleocene to late Early Eocene (D. P.
Smith in Abbott er al., 1995).

Unit contains fossiliferous marine sandstones and siltstones. Type sec-
tion is near Rancho Bateque, south of San Ignacio in the Mesa Las
Lagunitas quadrangle (Text-fig. 13). D. P. Smith er al. (1993a,b) re-
stricted the Bateque Formation to the east side of Laguna San Igna-
cio and published a new name, Bahia Ballenas Formation, for the
Paleogene marine sediments of the Vizcaino embayment. Middle
Eocene.

Unit consists of blueschists, chert, and volcaniclastic strata that are
exposed in fault blocks on Isla Cedros. It crops out in the southern
half of the island and along the east coast between Arroyo San
Carlos and Gran Canon. Sedlock (1993) regarded it as part of the
upper plate of the Choyal oceanic terrane. Middle to Late Jurassic
age.

Formation includes marine volcanic rocks and small granitoid plutons
that crop out on eastern Isla Cedros from Arroyo Choyal north-
ward. Part of the upper plate sequence of the Choyal oceanic ter-
rane. Jurassic, based on dates of 166-160 Ma (Sedlock, 1993).

Unit includes argillite, chert, limestone, sandstone, and a tuff dated at
159 Ma (Gastil er al., 1978; Sedlock, 1993). Well-exposed on both
flanks of a syncline in the southern part of Isla Cedros, it is part of
the upper plate sequence of the Choyal oceanic terrane (Sedlock,
1993). Middle to Late Jurassic.

Unit is a bathyal conglomerate that was deposited in a submarine
canyon. Type section in the southern Vizcaino peninsula is several
kilometers inland from Punta Abreojos, in the quadrangle of the
same name. Late Cretaceous age, Upper Campanian Stage (Drake,
1995):

Formation is a coarse-grained submarine conglomerate and sandstone.
Type area near Punta Eugenia, northwestern Vizcaino peninsula,
was not formally specified. It is the uppermost unit of the Vizcaino
Norte oceanic terrane (Sedlock, 1993). Late Jurassic to Early Creta-
ceous age, Tithonian to Valanginian Stage, based on the Tithonian
index fossil Buchia piochti (Gabb) and radiolarians (Hickey, 1984).

Table 4.—Continued.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 33

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Gran Canon formation,
informal name

La Costa Ophiolite

Los Chapunes forma-
tion, informal name

Los Cuervitos lime-
stone, informal name

Malarrimo Formation

Morro Hermoso
ophiolitic complex,
informal name

Morro Redondo forma-
tion, informal name

Perforada sandstone,
informal name

Pinos Formation

Puerto Escondido tuff,
informal name

Kilmer (1963, 1966, 1977). D.
A. Barnes (1984), Busby-
Spera (1988), Kimbrough
(1984), and Sedlock (1993)

also discussed.

T. E. Moore (1983, 1986). See
also Sedlock (1993).

Patterson (1984) used name for
the lower member of the Valle
Formation of Mina-Uhink
(1957). D. P. Smith et al.
(1993a) included in the Valle
Group.

D. P. Smith in Abbott er al.
(1995) named as member of
the Bahia Ballenas Formation.

Mina-Uhink (1957). Robinson
(1975, 1979a) and later work-
ers included in the Valle For-
mation.

Rangin (1979). Also called the
“tuff of Morro Hermoso”™ of
T. E. Moore (1986).

Kilmer (1979, 1984) name for
part of the Valle Formation of
Mina-Uhink (1957). D. P.
Smith er al. (1993) included as
a lithologic unit in the Pinos
Formation.

Hickey (1984). D. P. Smith ef al.
(1993) regarded as a formation
in the Valle Group.

D. P. Smith er al. (1993a), new
name for the upper part of the
Valle Group on Isla Cedros.
Formation contains five mem-
bers and the Morro Redondo
formation of Kilmer (1984).

D. A. Barnes (1982) named as
informal member of the San
Hipolito Formation. T. E.
Moore (1986) included in the
tuff at Morro Hermoso.

Unit includes tuff, voleanogenic breccia, and pyroclastic flows de-
scribed trom Gran Canon, northeastern Isla Cedros (Busby-Spera,
1998; Busby er al., 1998). In depositional contact with the Choyal
formation and the Cedros ophiolite, it is part of the upper plate se-
quence of the Choyal oceanic terrane (Sedlock, 1993). Late Middle
Jurassic.

La Costa Ophiolite includes chert, limestone, and volcaniclastic sedi-
ments. It is the oldest part of the basement complex in the southern
Vizeaino peninsula, part of the Choyal oceanic terrane (Sedlock,
1993), and overlain by the Late Triassic—Early Jurassic San Hipoli-
to Formation. Middle to Late Triassic.

Unit is a turbidite deposit described from a composite section (not
formally designated) northeast of Bahia Tortugas, in the Bahia Tor-
tugas quadrangle. It also crops out in the southern Vizcaino penin-
sula in Arroyo Pitahaya and Arroyo San Lorenzo, east of Punta
San Hipolito. Late Early Cretaceous age, Albian Stage, based on
foraminifers (Patterson, 1984).

Member is a 10-m-thick biosparrudite with coarse-grained sand- to
pebble-sized clasts that are mainly broken shells. Type section is a
ridge near Rancho el Carrizo, at 27°00° N, 26.8 km northeast of
Punta Abreojos in the Punta Abreojos quadrangle. Late Early Pa-
leocene to early Late Paleocene, based on fossils.

Formation is a conglomerate interbedded with sandstone and clay-
stone that crops out along the north coast of the Vizcaino peninsula
west of Punta Malarrimo, and from Arroyo de la Mesita to six ki-
lometers south (Text-figs. 6, 10). Originally regarded as Paleocene—
Eocene (Mina-Uhink, 1957), later revised to Cretaceous (Robinson,
1975).

Ophiolites and tuffs were described at Morro Hermoso, between Ba-
hia Tortugas and Puerto Nuevo in the Puerto Nuevo quadrangle.
They overlie the Sierra de San Andrés ophiolite. Late Triassic age
(T. E. Moore, 1986).

Unit consists of siltstone, sandstone, shale, and fossiliferous marine
conglomerate. Type section is exposed in central Isla Cedros in the
Punta Prieta and Arroyo Coloradito areas (Kilmer, 1984). Late Cre-
taceous age, Turonian Stage.

Rocks are fine-grained marine sandstones and siltstones named for a
section near La Perforada along the La Bamba Fault in the north-
ern Vizcaino Peninsula, Punta Eugenia quadrangle. Late Early Cre-
taceous age, Aptian—Albian Stage, based on radiolarians and fora-
minifers (Hickey, 1984), correlative with the Asuncion formation
(D. P. Smith, written communication, 1998).

Formation is a coarse-grained unit with rapid facies variations and
slump deposits, its stratigraphy complicated by syndepositional ac-
tive faults (D. P. Smith er al., 1993a). Type section is in the central
part of Isla Cedros, from Arroyo Choyal to Arroyo Vargas and near
Punta Prieta, where it overlies the Vargas Formation and Gran Can-
6n formation. It is overlain with angular unconformity by diatoma-
ceous beds of the Miocene Tortugas Formation. Early Late Creta-
ceous age, Lower Cenomanian Stage.

Unit consists of 200-300 m of tuffaceous chert, limestone, volcani-
clastic sandstone and tuff. It is well exposed in the walls of Arroyo
Puerto Escondido, also found at Morro Hermoso and to the north at
Punta Quebrada. Late Triassic age, upper Middle Norian Stage
based on radiolarians, conodonts, and well-preserved Monotis sp.
from calcareous tuff beds (Davila~Alcocer and Pessagno, 1986; D.
A. Barnes, 1984).

Table 4.—Continued.

BULLETIN 371

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

San Hipolito Forma-

tion

Santa Clara Formation

Sierra de San Andrés
ophiolite, informal

name

Tortugas Formation

Valle Formation, Valle

Group

Vargas Formation

Mina-Uhink (1957). Finch and

Abbott (1977), and Finch et
al. (1979) divided into four
members.

Mina-Uhink (1957).

T. E. Moore (1976, 1986).

Mina-Uhink (1957). Helenes-Es-

camilla (1980) recognized
Members A and B at Bahia
Tortugas and Members 1-4 at
Punta Quebrada, 10 km to the
west-northwest.

Mina-Uhink (1957). Later work-

ers divided into a number of.
different units. D. P. Smith er
al. (1993) raised to the Valle
Group, including the “undivid-
ed Valle Group™ (work in pro-
gress by D. P. Smith er al.,
written communication, 1998)
and the following: Pertorada
formation, Asuncion forma-
tion, Los Chapunes formation,
Vargas Formation, Pinos For-
mation, Conglomerados los
Juncos, and Bahia Ballenas
Formation.

D. P. Smith er al. (1993). New

name for the lower member of
the Valle Formation of Kilmer
(1984) on Isla Cedros and the
Los Chapunes formation of
Patterson (1984). D. P. Smith
et al. (1993) regarded as a for-
mation in the Valle Group.

Formation consists of 2,400 m of sediments and radiolarian chert di-
vided into four members, oldest to youngest: red and green fossilif-
erous chert, fossiliferous limestone, breccia, and volcaniclastic
sandstone with fossiliferous limestone concretions. Type locality,
not formally specified, is at the southern end of Punta San Hipolito,
approximately 40 km southeast of Asuncion, Bahia Asuncion quad-
rangle. Late Triassic, Norian Stage lower members, based on radio-
larians and hemipelagic pectinaceans in the genera Monotis and
Halobia. Early Jurassic age, Pliensbachian and/or Toaracian Stage
for the uppermost sandstone member, which contains radiolarians
and conodonts (Whalen and Pessagno, 1984; Whalen and Carter,
2002).

wrmation is a |120-m-thick agglomerate and reddish to purple volca-

nic breccia described from the Sierra de Santa Clara, inland from

Punta Abreojos in the southeastern Vizcaino peninsula. Mina-Uhink

(1957) regarded it as equivalent in age and origin to the San Zacar-

ias Formation, which he considered younger than the Eocene Ba-

teque Formation and probably Oligocene or Early Miocene.

Unit consists of ophiolitic rocks including pillow basalts and breccias.
Type area of this basement complex is south of Bahia Tortugas in
the Puerto Nuevo quadrangle. Part of the Vizcaino Norte oceanic
terrane, these rocks are older than the overlying conformable Late
Triassic tuff, chert, and volcaniclastic sandstone (Sedlock, 1993).

Formation is a 400-m-thick marine lithic sandstone overlain by diato-

maceous shales. Its type section consists of 45 m of neritic silty
sandstones and pelletal phosphorite (Member A) overlain by 95 m
of silty, diatomaceous shales (Member B); it is located east of the
airfield 2 km north of the town of Bahia Tortugas in the quadrangle
of the same name. Late Early Miocene to Middle Miocene (18-15
Ma to 15-10 Ma) at the type area, based on diatoms, benthonic
foraminifers, and mollusks (Helenes-Escamilla, 1980; Ingle, written
communication, 1984; Smith, 1984). The section at Punta Quebrada
ranges from late Early Miocene age, Upper Saucesian Stage to Late
Miocene age, Upper Mohnian Stage (18-15 Ma to 9.8—5.5 Ma)
(Helenes-Escamilla, 1980).

Formation has various lithologies, including fossiliferous mudstone,
siltstone, sandstone, and a massive sandstone with mudstone inter-
beds. Type area, not formally designated, is in a west-flowing ar-
royo in Valle Salitral, 4-5 km northeast of Bahia Tortugas in the
quadrangle of the same name (Robinson, 1975, 1979a). As a Group
of formations, the Valle is more than 8 km thick; it is mainly Late
Early Cretaceous age, Upper Albian Stage but may range to Early
Paleogene in some sections (D. P. Smith, written communication,
2000).

Formation is a fine-grained, shale-rich unit that attains a thickness of
1,700 m and is conformably overlain by the Pinos Formation. Type
locality is on east side of Isla Cedros, along the steep western wall
of Gran Canon. Unit is no younger than early Late Cretaceous, Tu-
ronian Stage (D. P. Smith, written communication, 1998).

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 35

Carter (2002), Troughton (1974), J. T. Smith (1984),
and T. E. Moore (1986). Area is shown on the Puerto
Nuevo quadrangle, G11B38, San Roque quadrangle,
G11B48, Bahta Asuncion quadrangle, G1 1B49, Estero
la Bocana quadrangle, G12A51, Punta Abreojos quad-

rangle, GI12A52, 1:50,000; and the geologic maps of

Troughton (1975), Finch and Abbott (1977), T. E.
Moore (1983), Whalen and Pessagno (1984), Drake
(1995), and D. P. Smith and students (ongoing field
work).

Mesozoic stratigraphy

Sierra de San Andrés ophiolite, informal name,
Middle to Late Triassic.—The Sierra de San Andrés
ophiolite basement complex of T. E. Moore (1976,
1986) described from the Puerto Nuevo area consists
of Middle to Late Triassic pillow basalts, cherts, and
breccias of the La Costa ophiolite sequence. These
rocks are overlain by Late Triassic to Early Jurassic
tuff, chert and volcaniclastic sandstone (Sedlock,
1993).

San Hipolito Formation, Late Triassic to Early Ju-
rassic.—Punta San Hipolito les 40 km to the south-
east of Asuncion; it is formed of sediments and radi-
olarian chert of the San Hipolito Formation, which is
restricted to this area. Of its four members, the two
oldest contain Late Triassic Norian Stage radiolarians
and the hemipelagic pectinaceans Monotis sp. cf. M.
subcircularis (Gabb) and Halobia lineata of authors
(Pessagno et al., 1979; Finch et al., 1979). Formerly
regarded as Triassic, the upper volcaniclastic sandstone
with limestone concretions contains abundant Early
Jurassic age, Plensbachian and/or Toarcian Stage
(195.3—180.1 Ma) radiolarians and conodonts (Whalen
and Pessagno, 1984; Whalen and Carter, 2002). The
San Hipolito Formation is part of the Vizcaino Sur
terrane that originated in an oceanic island arc setting;
it is in fault contact with the overlying Valle Group.

Valle Group, late Early Cretaceous.—The Valle
Group unconformably overlies basement rocks of the
Sierra de San Andrés-Cedros complex in the area from
San Roque to Asuncion (Rangin and Carrillo-Marti-
nez, 1978; T. E. Moore, 1984). Mapping and prelimi-
nary sedimentological studies in progress between
Asuncion and Punta Abreojos by D. P. Smith and stu-
dents will define five new formations within the Valle
Group, which attains 6 km of thickness in that area
(D. P. Smith er al., 1993a).

One of the units is the Conglomerados Los Juncos,
a localized upper Campanian Stage, Late Cretaceous
submarine-canyon deposit that is correlative with the
Perforada formation, informal name, of the northern

Vizcaino peninsula (D. P. Smith, written communica-
tion, 1998).

Bahia Ballenas Formation, Paleocene to Early Eo-
cene. Los Cuervitos limestone member, informal name,
Middle Paleocene.—D. P. Smith in Abbott er al.
(1995) provided new fossil data and descriptions for
the Middle Paleocene to late Early Eocene Bahia Bal-
lenas Formation. One of its shell beds is the Middle

Paleocene Los Cuervitos limestone, which crops out
north of Punta Abreojos and correlates with limestones
in the Sepultura Formation and parts of the Sierra
Blanca Limestone in southern California (Abbott er
al., 1995; Saul, 1983). The Middle Paleocene age is
based on the molluscan index species Turritella pen-
insularis Anderson and Hanna, Turritella infragranu-
lata pachecoensis Stanton, Venericardia venturaensis
Verastegui, and Venericardia sp. cf. V. nelsoni Ver-
astegui, which also correlate it with the lower part of
the Santa Susana Formation in the Simi Hills of south-
ern California.

Tortugas Formation, late Early to Middle Mio-
cene.—Arroyos north and east of the town of Asun-
cion were mapped by Troughton (1974), who delin-
eated unnamed fine phosphatic beds overlain by diat-
omite as the Tortugas Formation. Samples of diato-
maceous shales from the “‘Valle de Diatomita’ or
Arroyo la Chiva (10 km northwest of Bahra Asuncion
and 2 km east of the road to Punta San Roque, San
Roque quadrangle) yielded early Late Miocene (8.9—
8.4 Ma) diatoms of Denticulopsis hustedii Subzone D
and the D. lauta Zone (Moreno-Ruiz and Carreno,
1993, locality IGM-2439, 27°11'29" N, 114°20'55”
W), and Late Miocene Diartus petterssoni and Didy-
mocyrtis antepenultima radiolarian zones (Pérez-Guz-
man, 1985). In this area the unit is also known for
shark teeth, fish, and mammals (Applegate er al.,
1979).

A localized well-indurated sandstone on the beach
at Asuncion has different megafossils but seems refer-
rable to the lower part of the Tortugas Formation. Mol-
lusks include Amussiopecten vanvlecki (Arnold) and
large Turritella sp.

Almejas Formation, Late Miocene.—D. P. Smith
and others have mapped the Almejas Formation in the
area of Punta Abrojos, where it overlies the Cretaceous

Valle Formation with angular unconformity. Recon-
naissance collections of Late Miocene megafossils in-
clude Lyropecten gallegosi (Jordan and Hertlein) and
Leptopecten praevalidus (Jordan and Hertlein).

36 BULLETIN 371

Western embayment, northern part,
Arroyo San Ignacio, Arroyo Patrocinio,
Arroyo San Raymundo
Plate 1, Columns 13, 14, 15
(Text-figs. 2, 13-16, 18, Appendices 1, 2)

Columns modified from Mina-Uhink (1957), Mc-
Lean et al. (1985, 1987), Squires and Demetrion
(1992). Area is shown on the San Ignacio quadrangle,
G12A34, Mesa las Lagunitas quadrangle, G12A43, El
Patrocinio quadrangle, G12A54, San Juan quadrangle,
G12A65, San Raymundo quadrangle, G12A75, scale
1:50,000; and the geologic maps of McLean er al.
(1985), 1:125,000; McLean and Hausback (1984),
scale 1:83,000; Mina-Uhink (1957), scale 1:500,000;
and Beal (1948).

Overview

The region that includes Arroyo San Ignacio and
Laguna San Ignacio is the northern part of an Early
Eocene to Miocene embayment that extended from
this area of western Baja California to the southern
Magdalena Plain. Marine formations that are penecon-
temporaneous with units in the Magdalena Plain are
gently folded, north to south, and capped by extensive
Miocene tholeiitic basalts (1O—6 Ma) that emanated
from near San Ignacio (Sawlan and Smith, 1984; Saw-
lan, 1991). There are no Mesozoic basement rocks ex-
posed in the western embayment, although McLean er
al. (1987) noted dioritic and granitic clasts in a basalt
flow in Arroyo la Purisima, upstream from San Isidro.

From north to south, significant outcrop areas are
exposed by streams flowing west from the crest of the
Sierra la Giganta in Arroyo San Ignacio, Arroyo Pa-
trocinio, and Arroyo San Raymundo, among others.
The southernmost exposures of Eocene diatomite on
the Pacific coast occur in Arroyo San Raymundo.

Arroyo San Ignacio
Plate 1, Column i3
(Text-figs. 2, 10, 13-15, Appendices 1, 2)

Column modified from Mina-Uhink (1957); area 1s
shown on the San Ignacio quadrangle, G12A34 and
the Mesa las Lagunitas quadrangle, G12A43, scale
1:50,000; and the geologic maps of Mina-Uhink
(1957) and Beal (1948).

Stratigraphy

Bateque Formation, Early Eocene.—The marine
Bateque Formation of Mina-Uhink (1956, 1957) is an
arkosic sandstone and siltstone. Although a specific
outcrop was not designated, it was named for a section
near Rancho Bateque, 32 km southwest of San Igna-
cio, Mesa Las Lagunitas quadrangle (Text-fig. 13). Its

age, based on microfossils and megafossils, is Early to
late Middle Eocene (Sorensen, 1982; McLean er al.,
1987; Squires and Demetrion, 1992; Squires, 1997).
The Early Eocene index species Turritella andersoni
Dickerson identifies the unit in the type area as “*‘Ca-
pay” West Coast Molluscan Stage (Squires, 1988). It
crops out for 70 km from the east side of Laguna San
Ignacio to Batequi de San Juan, and discontinuously
as far south as Arroyo Mezquital, east of Punta Pe-
quena (McLean er al., 1985).

Correlation

The Bateque Formation correlates in part with the
upper Tepetate Formation, which crops out 200 km to
the south in the Magdalena Plain. Squires and Deme-
trion (1992) referred the Bateque Formation to the
“Capay’> West Coast Molluscan Stage at its type area,
but to a younger, late Middle Eocene age, “Tejon”
West Coast Molluscan Stage at Arroyo Mezquital.

Paleogene marine units of Mina-Uhink (1957): San
Zacartas, Santa Clara, Zorra and San Joaquin For-
Southeast
of Laguna San Ignacio in the area between Rancho
San Joaquin and mesas near Cuarenta the Bateque For-
mation is overlain unconformably by several Oligo-
cene to Miocene units named by Mina-Uhink (1957):
the San Zacarias, Santa Clara, Zorra and San Joaquin
Formations. Some might be penecontemporaneous. Of
limited geographic extent, they include volcanic brec-
cias and mesa-capping deposits that have not been vis-
ited since Mina-Uhink’s work. Their type areas were
given, respectively, as: Arroyo San Joaquin, near Ran-
cho San Zacarias; mesa tops in the Sierra de Santa
Clara, Rancho el Alamo and Casa Blanca (the shallow
marine Zorra Formation); and continental deposits
near Rancho San Joaquin. A period of erosion or non-
deposition separated these units from subsequent shal-
low marine deposits.

mations, Oligocene (?) or Early Miocene.

San Ignacio Formation, late Middle Miocene to
Late Miocene.—The San Ignacio Formation is a white,
fossiliferous, calcareous, and volcaniclastic marine
sandstone named by Mina-Uhink (1957) for cliffs
along Arroyo San Ignacio. Beal (1948) and later work-
ers regarded the type area as 4—8 km downstream from
the town of San Ignacio (Text-figs. 14, 15). Facies in-
clude limy marls, coquina, siltstone, and coarse pebbly
sandstone.

Abundant shallow-water marine fossils were report-
ed by Hertlein and Jordan (1927), Beal (1948), and J.
T. Smith (1984, 1986). Hertlein and Jordan (1927) de-
scribed, among others, Thais wittichi, Macron hart-

manni, Cymia heimi, Turritella boései, Chione richtho-

feni, Sanguinolaria toulai, and Amiantis sp. These taxa

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 37

7 San Ignacio 27° 15'N

. v6 fe San Joaquin
2 x ;
2 bet -m@’ San Zacarias
Sierra de 7 Ay Zt
Santa Clara aS @ Bateque
e v/ |
= ‘ 27° 00'N

/
I
| Laguna
; San Ignacio
I
!
!
I
/

Mesa el Yeso
x... Arroyo Patrocinio
-@ Rancho Patrocino

Mesa las Salinas 26° 45'N

Cuarenta

waa las
<— Gallinas

San José
*de Gracia

Arroyo San
Raymundo

“go. Bateque de
San Juan

26° 15'N

Mexico highway |

& Outcrops of Bateque Formation
‘= Rancho - Ranch

e Town/village
Unpaved road

0 15 KM
=

113° 15'W 112° 30'W

Text-figure 13.—Western embayment, San Ignacio to Arroyo Mezquital, with outcrops of the Eocene marine Bateque Formation. Map is
modified from Squires and Demetrion (1992).

Text-figure 14.—Arroyo San Ignacio, view from Rancho el Estribo at type area of the Late Miocene San Ignacio Formation, 4-8 km
downstream from San Ignacio. Photo, T. M. Cronin, 1984.

San Ignacio Formation, south wall of Arroyo San Ignacio showing fossiliferous marine sediments overlain by an unnamed

Text-figure 15.
volcaniclastic sandstone (possibly the Atajo Formation of Mina-Uhink, 1957) and capped by the Late Miocene basalt of Rancho Esperanza.
Photo, T. M. Cronin, 1984.

Text-figure 16.—Mesa el Yeso, north side of Arroyo Patrocinio. White fossiliferous sandstones of the Isidro Formation are overlain by a
thin layer of Comondu Formation and capped by basalts with a K/Ar age of 8.1 + 0.4 Ma. Photo, J. R. Ashby, Jr.

Text-figure 17.—Arroyo Mezquital section of Eocene Bateque Formation siltstones overlain unconformably by the Miocene Isidro Formation.
Beal (1948) mapped the units as Eocene Tepetate Formation overlain by the Miocene Salada Formation. Photo, J. T. Smith, 1984.

38 BULLETIN 371

need to be compared with Tertiary-Caribbean taxa to
determine their faunal affinities. The late Middle to
Late Miocene age is based on megafossils and a ra-
diometric age of 9.72 + 0.29 Ma for the overlying
basalt of Rancho Esperanza (informal name) exposed
along Mexico | near the road to San Lino, between
Microondas Abulon and the turn-off to San Ignacio
(Text-fig. 10, herein; Sawlan and J. G. Smith, 1984; J.
T. Smith, 1986). In places the marine beds are overlain
by an unnamed volcaniclastic sandstone that is capped
by the basalt (Sawlan and J. G. Smith, 1984) (Text-
fig. 15).

The San Ignacio Formation crops out from just
north of Mexico | at San Ignacio to north of Arroyo
Patrocinio. Although Mina-Uhink (1957) mapped the
formation as far as Mesa Cuarenta, 50 km south of the
type area, McLean ef al. (1985, 1987) interpret the
fossiliferous sandstone at Arroyo Patrocinio and to the
south as the older Miocene Isidro Formation. Yellow-
ish-brown sandstones and siltstones near Rancho San
Angel, 24 km southwest of San Ignacio, Mesa las La-
gunas quadrangle, are probably another facies of the
San Ignacio Formation; they contain abundant external
molds of marine mollusks (Beal, 1948; J. T. Smith,
1986).

Correlation

Although there are some molluscan fossils in com-
mon between the San Ignacio Formation and the Isidro
Formation, the former could be younger by several
million years. The Isidro Formation is inferred to be

Early Miocene to late Middle Miocene on the basis of

fossils and the radiometrically dated tuffs in the over-
lying Comondu Formation; the San Ignacio Formation
could be latest Middle to Late Miocene, based on me-
gafossils and the age of the overlying basalt of Rancho
Esperanza (Sawlan and J. G. Smith, 1984; Sawlan,
1991; J. T. Smith, 1986). The San Ignacio Formation
correlates with the Tortugas Formation of the adjacent
Vizcaino embayment, although the two units differ
markedly in lithology, megafaunal composition, and
depositional history.

Atajo Formation, Miocene.—Mina-Uhink (1956,
1957) named but did not describe the Atajo Formation
as an unconformable volcaniclastic unit in the area
north of Cerro San Angel between the Vizcaino pen-
insula and San Ignacio. He regarded it as a local equiv-
alent of the Late Miocene Comondu Formation and
uncontormable above the San Ignacio Formation. The
name has not been used or investigated since then,
although it may be appropriate for an unnamed vol-
caniclastic sandstone that overlies the San Ignacio For-

mation in the eastern wall of Arroyo San Ignacio
(Text-fig. 15).

Basalt of Rancho Esperanza, informal name, Late
Miocene.—Sawlan (1991) discussed a young tholetitic
basaltic andesite, the basalt of Rancho Esperanza (in-
formal name of Sawlan and J. G. Smith, 1984), which
is 3—6 m thick and has a K/Ar age of 9.7 + 0.29 Ma
near San Ignacio. The distinctive, fast-flowing lava
erupted in the area of Rancho Esperanza near the Tres
Virgenes volcanoes (Text-fig. 49) and extended south-
west as far as the Pacific Ocean, where it formed pil-
lows at Punta Pequena (Sawlan, 1991, fig. 4).

Arroyo Patrocinio
Plate 1, Column 14
(Text-figs. 10, 13, 16, Appendices 1, 2)

Column is modified from McLean er al. (1985,
1987) and Squires and Demetrion (1992). Area is
shown on the El Patrocinio quadrangle, G1 2A54, scale
1:50,000; and the geologic maps of McLean ef al.
(1985), scale 1:125,000; McLean and Hausback
(1984); Mina-Uhink (1957); and Beal (1948).

Overview

Marine sections from Arroyo Patrocinio to Punta
Pequena are capped by volcanic units whose Late Mio-
cene dates constrain the underlying sediments. Arroyo
Patrocinio is approximately 60 km south of San Ig-
nacio, accessible by a challenging, unpaved, ungraded
road famous for sandy “brincas malas.” The region
contains the northernmost thin outcrops of the Isidro
and Comondu Formations described from the Puritsi-
ma-Iray basin 140 km to the south; the type section of
the Eocene Bateque Formation is just north of this
area. Mesa el Yeso flanks the mouth of Arroyo Patro-
cinio on the north, Mesa la Salinas on the south (Text-
fig. 16).

Stratigraphy

Bateque Formation, Early Eocene.—The Bateque
Formation crops out in Arroyo Patrocinio, where it is
unconformably overlain by the Isidro Formation, Mio-
cene capping basalts, or late Tertiary to Quaternary
gravels (McLean er al., 1987). In this area it is Early
Eocene age, “Capay’> West Coast Molluscan Stage
based on Turritella andersoni Dickerson and other
species (Squires and Demetrion, 1992, 1994a).

Isidro Formation, late Middle Miocene.—Described
from the area of La Purisima and San Isidro, the Isidro
Formation is a highly fossiliferous shallow-marine
clastic unit that thins to the northeast to perhaps a few
tens of meters on the north side of Arroyo Patrocinio.
It can interfinger with the lower San Ignacio Formation

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 39

to the north (McLean er al., 1987). The section at Mesa
el Yeso is overlain unconformably by a thin layer of
the Comondu Formation, also described from the Si-
erra la Giganta, and by Late Miocene basalt flows
whose ages are 8.4 + 0.30 Ma (J. T. Smith, 1991c, p.
645) and 8.1 + 0.4 Ma (McLean ef al., 1985, 1987).
Megafossils and radiometric ages of associated rocks
suggest its age in Arroyo Patrocinio is late Middle
Miocene, penecontemporaneous with or slightly older
than the San Ignacio Formation.

Comondu Formation, Late Miocene.—McLean et
al. (1985) mapped the northernmost occurrences of the
Comondu Formation in Arroyo Patrocinio. A fluvial
volcaniclastic conglomerate, the unit has been widely
interpreted by many authors to include volcanic rocks
and vent facies from eastern Baja California Sur be-
tween Santa Rosalia and La Paz. We use a narrower
definition for this formation, which we discuss in the
section on the Purisima-Iray basin, p. 44. The Com-
ondu Formation is 1,800 m thick at its type area near
San Jose de Comondu, but only a few meters thick at
Arroyo Patrocinio. Its age is constrained at Mesa las
Gallinas by an overlying basalt flow with a #°Ar/°Ar
age of 10.05 + 0.4 Ma (Text-fig. 13, herein; McLean
et al., 1985, 1987).

Arroyo San Raymundo
Plate 1, Column 15
(Text-figs. 2, 13, 18, Appendices 1, 2)

Column modified from McLean et al. (1985, 1987).
Area is shown on the San Juan quadrangle, GI2A65,
and the San Raymundo quadrangle, GI2A75, scale
1:50,000; and the geologic maps of McLean er al.
(1985), scale 1:125,000; McLean and Hausback
(1984); Mina-Uhink (1957); and Beal (1948).

Stratigraphy

Bateque Formation, Middle Eocene.—The Bateque
Formation in Arroyo San Raymundo consists of
brown, thin-bedded arkosic sandstones and siltstones
interbedded with white diatomites and siliceous shales
that contain cool-water, upper bathyal taxa of latest
Middle Eocene age. The diatoms indicate the 7ricer-
atium inconspicuum var. trilobata Partial Range Zone
(McLean and Barron, 1988).

Significant outcrops are seen upcanyon from where
Arroyo San Raymundo crosses the unpaved road from
Cadaje to San José de Gracia. The locality is approx-
imately 20 km north of Punta Pequena and north of
latitude 26°15’ N (Text-fig. 18). According to McLean
and Barron (1988), it is the southernmost occurrence
of Eocene diatomite known in North America, correl-
ative with the Kreyenhagen Shale of California.

The Bateque Formation is overlain unconformably
in Arroyo San Raymundo by the northernmost expo-
sures of the Late Oligocene San Gregorio Formation.
Squires and Demetrion (1992) suggested that more de-
tailed mapping might place the diatomite in the lower
part of the San Gregorio Formation, whose base is not
exposed, rather than in the Bateque Formation.

San Gregorio Formation, Late Oligocene to Early
Miocene.—In Arroyo San Raymundo the San Grego-
rio Formation consists of phosphatic and_ siliceous
shale, sandstone, and an interbedded tuff of 21.9 + 0.8
Ma (Hausback in McLean et al., 1985). Regarded as
Oligocene at its type area, these beds are interpreted
as Early Miocene middle and outer shelf deposits that
are unconformably overlain by shallow water sedi-
ments of the Isidro Formation.

Isidro. Formation, Middle Miocene.—Mina-Uhink
(1957) named this unit the San Raymundo Formation,
but subsequent mappers regard it as the earlier-named
Isidro Formation described by Heim (1922) from the
village of La Purtsima. The grayish-white marine
sandstone and siltstone contains well- to poorly-pre-
served shallow-water to inner-shelf megafossils. It is
overlain unconformably by the nonmarine Comondu
Formation. Mina-Uhink (1957) mapped the Isidro For-
mation from the Vizcaino peninsula to approximately
75 km north of La Paz, noting lateral facies changes
from shales to sandstones. More recent mapping limits
the formation to outcrops between Arroyo Patrocinio
and Arroyo la Purtsima.

Comondu Formation, late Middle Miocene.—De-
scribed from farther south, the Comondu Formation in
this area is a brown to gray, poorly sorted volcani-
clastic sandstone and conglomerate deposited by braid-
ed streams. An interbedded basalt flow in Arroyo San
Martin, the next drainage southeast of Arroyo San
Raymundo, yielded a K/Ar age of 12.9 + 0.7 Ma (Mc-
Lean et al., 1985; Text-fig. 18 herein). An unconfor-
mity separates the Comondu Formation from overlying
plateau basalts.

Unnamed plateau basalts, Late Miocene.—Wide-
spread unnamed plateau basalts cap the section over
much of the western slopes. McLean et al. (1987) re-
ported a K/Ar age of 10.7 + 1.14 Ma for a pillow
basalt in Arroyo San Raymundo.

Purtsima-Iray basin, western slopes of the
Sierra la Giganta, Western embayment
Plate 1, Column 16
(Text-figs. 2, 17-23, Appendices 1, 2)
Column modified from McLean er al. (1987). Area
is shown on the San Raymundo quadrangle, G12A75,

40 BULLETIN 371

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Y XS J Purisimag’ yy° a
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S 1 Vieja Paso Hondo 2
~ wae ( Le
WY LyYv ‘ 5 - Ary, =
Nees LA El Pilon ~~9 7 =
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mN \ “Vv Pe SG y
= La Pur : ;
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= { Le San } Rosarito
S a Isidro : at
a 2 :
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San José de-*
y 4Comondu

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 4]

Paso Hondo quadrangle, G12A76, San Isidro quadran-
gle, GI2A76, Punta Pequena quadrangle, G1I2A85,
Comondu quadrangle, GI2A87, scale 1:50,000; and
the geologic maps of Beal (1948), McLean and Haus-
back (1984), McLean er al. (1985), and Mina-Uhink
(1956; T9577):

Overview

The Purtsima-Iray basin was named by Mina-Uhink
(1956, 1957) for the 16,000 km? area from Arroyo la
Purisima to La Paz. For convenience we restrict this
basin to the area between Arroyo Patrocinio and the
vicinity of Colonia Santo Domingo. The western
slopes of the Sierra la Giganta are underlain by a flat-
lying to gently dipping Middle Eocene to Middle Mio-
cene marine section that was slightly deformed from
north to south. Many deep southwest-trending canyons
provide good exposures of the section.

La Purisima is an old village along Arroyo la Pur-
isima, 4 km downstream from the newer town of San
Isidro. Iray is named for Pozo Iray #1, a Pemex petro-
leum well at Colonia Santo Domingo, north of Ciudad
Constitucion and south of La Poza Grande (Text-fig.
56). The area was mapped in 1918 as a potential
source of onshore oil reserves by Beal’s Marland Oil
Company survey (published by Anonymous, 1924,
and Beal, 1948) and by Mina-Uhink in 1943 for Pe-
trodleos Mexicanos or Pemex (published by Mina-
Uhink, 1956, 1957). Data from Pozo Iray #1 and other
wells provided subsurface geology for Mina-Uhink’s
map. Granitoid and metasedimentary basement rocks
are not exposed in the western slopes of the Sierra la
Giganta.

Zanchi et al. (1992) used regional unconformities to
separate the main sedimentary units in the La Purtsima
area. They preferred the terms Lower Sedimentary Se-
quence, Middle Sedimentary Sequence, and Upper
Sedimentary Sequence for the San Gregorio, Isidro,
and lower Comondu Formations of earlier mappers.

Stratigraphy

Santo Domingo Formation, Paleocene.—Mina-
Uhink (1957) gave the name Santo Domingo Forma-
tion to the oldest sediments he recovered from Pemex
well Pozo Iray #1, south of La Poza Grande (Text-fig.
56). He reported a maximum thickness of 1,366 m of
Paleocene gray shales with interbedded sands and
sandstone. Later workers have not recognized the unit.

Bateque Formation, late Middle Eocene.—Flat-ly-
ing, yellowish-brown sandstone and siltstone contain-
ing marine megafossils and large discocyclinid fora-
miniters are well exposed near the mouth of Arroyo
Mezquital in outcrops studied by Beal (1948), Mina-
Uhink (1957), and Squires and Demetrion (1992),
among others. Beal (1948) and Mina-Uhink (1957)
mapped the sediments as the Tepetate Formation,
which was described by Heim (1922) 200 km further
south. McLean ef al. (1985) and Squires and Deme-
trion (1994a) mapped them as the southernmost out-
crops of the Bateque Formation (Text-figs. 13, 18-20).

The Bateque Formation has an overall range of mid-
dle Early Eocene to late Middle Eocene (55—42 Ma).
Squires and Demetrion (1990a,b, 1992, 1994a,b) re-
fined the age on the basis of megafossils; they docu-
mented an older, late Early Eocene ““Capay” Stage

Text-figure 18.—Western embayment, south of Arroyo Patrocinio to San José de Comondu, map showing southernmost outcrops of Eocene
diatomite in western North America. Map modified from McLean er al. (1987) and McLean and Barron (1988). Middle Miocene K/Ar ages
for volcanic flows interbedded with the Comondu Formation are 14.5 * 1.2 Ma at Purtsima Vieja (McLean ef al., 1985, sample 15) and 12.9
+ 0.7 Ma in Arroyo San Martin (McLean er al., 1985, sample 10). V, La Ventana, area of lower Arroyo la Purisima where Hausback (1984b)
dated Late Oligocene rhyolite tuffs in the San Gregorio Formation as 25.5 + 0.4 Ma and 23.4 + 0.3 Ma (K/Ar samples 28-3-8 and 28-3-16,
respectively).

Text-figure 19.—Bateque Formation, Eocene foraminiferal facies in Arroyo Mezquital. The beds are composed mainly of the discocyclinid
Pseudophragmina advena (Cushman) but they also contain abundant Cubitostrea mezquitalensis Squires and Demetrion and Lepidocyclina sp.
(specimens on hammer); above them are fragments of the Eocene pectinid Batequeus mezquitalensis Squires and Demetrion and a Holocene
land snail. Photo, J. T. Smith, 1984.

Text-figure 20.—Contact between the Miocene Isidro Formation and underlying Eocene Bateque Formation marked by bulbous burrows,
Arroyo Mezquital. Photo, J. T. Smith, 1984.

Text-figure 21.—Phosphatic and diatomaceous beds of the Oligocene San Gregorio Formation exposed in Arroyo la Purtsima near the dam
(a presa) at San Isidro. Photo, T. M. Cronin, 1984.

Text-figure 22.—E] Pil6n, view northwest across Arroyo la Purisima from San Isidro. Oldest to youngest, the units are: San Gregorio
Formation in the bottom of the arroyo (Tsg), white Isidro Formation (Tsi, at right of photograph), Comondu Formation forming most of El
Pilon (Tc), and younger basalt capping the butte (Tb). Cinder cones to the right are 0.86 Ma (McLean er al., 1987). Photo, J. T. Smith, 1984.

Text-figure 23.—San José de Comondut, type area of Middle Miocene Comondt Formation. Lavas of several ages postdate the Comondu
Formation, the youngest flows filling the canyons and the oldest flows capping the mesa. Photo, J. G. Smith, 1982.

rig) BULLETIN 371

sequence in the northern area and a younger, late Mid-
dle Eocene, lower “Tejon” Stage in the Purfsima-Iray
basin. Microfossils at Arroyo Mezquital also indicate
this age (Carreno and Cronin, 1993).

At Arroyo Mezquital the Bateque Formation is un-
conformably overlain by yellowish-gray sediments of
Isidro Formation, the contact marked by a striking ho-
rizon of bulbous sediment-filled burrows (Text-fig. 20).

San Gregorio Formation, Late Oligocene.—Beal
(1948) named the San Gregorio Formation for a folded
section of white diatomaceous shale, phosphatic sand-
stone, tuff, and porcellanite exposed along the bottom
and walls of Arroyo la Purisima, from 4+ km down-
stream from the village of La Purisima to tidewater.
McLean er al. (1987) measured a thickness of 72 m
near the base of the butte El Pilon (Text-figs. 21, 22).
Early reconnaissance studies referred the unit to the
*“Monterey-Beds” (Darton, 1921), the “‘Monterey For-
mation,” or “‘Monterrey Formation” (Heim, 1922;
Mina-Uhink, 1957) because of lithologic similarities
to the younger oil-bearing Monterey Shale of Califor-
nia.

Topical paleontological studies by Kim (1986) and
Kim and Barron (1986) indicate a Late Oligocene age
for the diatomite in the San Gregorio Formation at La
Purtsima. Kim (1987) listed species from planktonic
foraminiferal zones P21 and P22, diatom zones Ro-
cella vigilans, Bogorovia veniamini, and Rocella gel-
ida, and equivalent calcareous nannotossil zones NP
24 to CP 19b (33 Ma—22.5 Ma, fide Barron er al.,
1985). Kim (1987) and Kim and Barron (1986) cor-
related the upper San Gregorio Formation with the lat-
est Oligocene—earliest Miocene Rocella gelida diatom
zone (23.5—22.5 Ma) at La Ventana. Microfossil ages
are corroborated by radiometric ages of 27.2 + 0.6 Ma
near the base of the exposed section in Arroyo San
Gregorio, 23.4 + 0.3 Ma and 23.9 + 0.4 Ma on an
interbedded tuff in the upper part of the formation at
La Ventana (Text-fig. 18, herein; Hausback, 1984b).

The San Gregorio Formation is exposed in discon-
tinuous outcrops between Arroyo San Raymundo and
Arroyo la Purisima, as mapped by McLean ef al.
(1985). The name was also used for penecontempor-
aneous sediments in the Magdalena Plain, until a paper
by Applegate (1986) introduced the name El Cien For-
mation for those sections. Further mapping and anal-
yses are needed to refine the correlation between the
two areas. The base of the San Gregorio Formation is
not exposed; its upper contact is an unconformity with
the Isidro Formation.

Isidro Formation, Early Miocene to early Middle
Miocene.—Shallow neritic yellowish-gray to white
sandstone, siltstone, and coquina were described by

Heim (1922) from the type locality “‘at Canal Head”
in Arroyo la Purisima, before the dam was built at
what 1s now the town of San Isidro. Referred infor-
mally to the ** Yellow beds” by Darton (1921), the Ysi-
dro Formation by Beal (1948), and the San Raymundo
Formation by Mina-Uhink (1957), the unit crops out
from the area of Arroyo Patrocinio to south of Arroyo
la Purtsima (Mina-Uhink, 1957; McLean er al., 1985),
and several kilometers east of the village of San Isidro.

The type section contains numerous biofacies and
abundant well-preserved invertebrate fossils, many
with Tertiary-Caribbean faunal affinities (J. T. Smith,
1984). These include the gastropods Turritella gatu-
nensis rhytodes Woodring, Turritella bifastigata Nel-
son, Melongena (Melongena) consors (Sowerby), Cy-
mia sp. ct. C. cheloma Woodring, Strombus sp. cf. S.
costatus Gmelin, Rapana imperialis Hertlein and Jor-
dan, and the bivalves Lyropecten pretiosus (Hertlein),
Spondylus scott’ Brown and Pilsbry, ““Aequipecten™
canalis (Brown and Pilsbry), Clementia dariena (Con-
rad), and Hyotissa haitensis (Sowerby). The Isidro
Formation is younger than 23 Ma, the age of a tuff
near the top of the underlying San Gregorio Forma-
tion, and older than 14.5 Ma, the age of a basalt flow
in the overlying Comondu Formation near Purisima
Vieja (Hausback, 1984a,.b: McLean er al., 1987).

The Isidro Formation is regarded as Early Miocene
to early Middle Miocene, 15—21.5 Ma, in the type
area, based on megafossils, microfossils, and con-
straining radiometric data. McLean er al. (1985)
mapped the contact between the Isidro Formation and
the Comondu Formation as a time-transgressive un-
conformity, older to the southeast and younger to the
northwest. McLean er al. (1987) reported that the Isi-
dro Formation interfingers with the Comondu Forma-
tion to the east. At Arroyo Patrocinio the Isidro For-
mation is disconformable on the Early Eocene Bateque
Formation and capped by Late Miocene basalt flows
that have radiometric ages of 8 Ma and 10 Ma (Mc-
Lean et al., 1987).

Beal (1948) referred the rocks above the Eocene
sediments at the mouth of Arroyo Mezquital to the
Salada Formation, because of the yellow color, lithol-
ogy, and abundant molluscan fossils. McLean ef al.
(1985) mapped the units as Bateque Formation and
Isidro Formation. Recent paleontological work sug-
gests that the upper Isidro Formation could indeed be
correlative with parts of the Salada Formation; detailed
mapping, well core data, and facies analyses would
help verify this correlation.

Beal (1948) mapped the Isidro Formation south of
the Magdalena Plain to San José del Cabo, but later
workers restricted it to the western embayment be-
tween Arroyo Patrocinio and the La Purisima area.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 43

Some authors suggested that it extended east to the
present Gulf of California; Helenes and Carreno
(1999) reported microfossil assemblages characterized
by mixed cool and tropical temperatures that could
support such a connection.

Purisima Nueva Formation, obsolete name, Early
Miocene to early Middle Miocene.—Heim (1922:
536-537) assigned folded beds 4—5 km downstream
from La Purisima to his **Purtsima Nueva Formation,”
but later workers included them in the Isidro Forma-
tion. Fossil assemblages are the same as elsewhere in
the unit; flat-lying and deformed beds within the for-
mation indicate synchronous deformation and deposi-
tion (McLean er al., 1987). Heim used an older name
for Arroyo la Purtsima: Arroyo Cadegomo. The stream
was also known as the San Ramon River. Beal’s un-
published map sheets, in Stanford University’s Branner
Earth Sciences Library and Map Collections, include
the local names for streams and old ranchos.

Correlation of Oligocene and Miocene units in the
Purtsima-lray basin

The San Gregorio and Isidro Formations are pene-
contemporaneous with parts of the El Cien Formation
of the Magdalena embayment, although exact corre-
lations have yet to be determined. Although the marine
parts of all these units are fossiliferous (Kim, 1987; J.
T. Smith, 1984, 1986; Gidde im Fischer et al., 1995),
most of the molluscan species are not the same. Ra-
diometric ages of volcanic rocks associated with the
San Ignacio Formation to the north suggest that the
Miocene unit is slightly younger than the Isidro For-
mation at its type area.

Comondu Formation, time-transgressive, late Mid-
dle Miocene to early Late Miocene.—Noted by Gabb
(1869a) as one of the mesa-forming units of the west-
ern Baja California peninsula, the Comondu Formation
was formally described in the western Sierra la Gi-
ganta by Heim (1922). He listed a number of sedi-
mentary facies—nearly horizontal fluvial sandstone,
mudstone, volcaniclastic breccia, and cobble to boul-
der conglomerate—exposed in canyons around the vil-
lage of San José de Comondu (Comondu quadrangle),
approximately 50 km west of Loreto and 40 km south-
east of La Purtsima. He emphasized that this is not a
volcanic unit. Deposited by braided streams, it 1s a
matrix-supported clastic unit whose volcanic clasts are
well-rounded rocks eroded from a volcanic arc that
was active from 24—12 Ma in the area of the present
Gulf of California (Sawlan, 1991).

The Comondu Formation is at least 1,800 m thick
along the crest of the Sierra la Giganta; it thins to the
north and west and and is younger at Arroyo Patro-

cinio, 175 km to the north (McLean er al., 1985; Mina-
Uhink, 1957). Constrained to 14.5—12 Ma in the La
Purisima area, the Comondu Formation at Mesa las
Gallinas is 10 Ma, capped by a basalt with a *’Ar/°Ar
age of 10.5 + 0.4 Ma (McLean et al., 1985) (Text-fig.
13, p. 37). Its southernmost extent is regarded by some
workers as the eastern Magdalena embayment, as
shown in regional maps of Tembabiche (or Tembabi-
chi) and San Juan de la Costa (p. 92).

Mina-Uhink (1957) and Hausback (1984) mapped it
as far south as the La Paz Peninsula; Martinez-Gutiér-
rez and Sethi (1997) showed the unit in the Cabo
Trough. The Comondu Formation is well exposed
along roads between Mexico | at Rosarito, north of
Loreto, and the town of San Isidro, and between Lor-
eto and Mision San Javier. It underlies La Giganta, at
1,765 m the highest point on the crest of the Sierra la
Giganta. McLean er al. (1987) discussed variations in
sedimentology, composition and age; McLean (1989)
chose to refer sediments in the onshore Loreto embay-
ment to proximal or distal facies, terms related to the
volcanic are source of the clasts, rather than to the
Comondu Formation.

Age of the Comondu Formation, late Middle Mtio-
cene.—The age of the Comondu Formation is time-
transgressive, no younger than capping flows of alkali
basalt dated at 8-14 Ma, according to McLean er al.
(1987). In the type area and to the northwest, most of
the unit was deposited in the late Middle Miocene,
between 14 and 12 Ma. This is documented by rare
interbedded ash-flow tuffs and alkalic basalt flows in
Arroyo San Martin, 20 km north of its junction with
Arroyo Cadajé, and at Purtsima Vieja, 4 km south of
Paso Hondo in Arroyo San Gregorio (Text-fig. 18).
Hausback (1984b) and McLean er al. (1987, figs. 10
and 12, and their Table 1) reported K/Ar ages of 12.9
+ 0.7 Ma and 14.5 + 1.2 Ma, respectively, for these
interbedded flows.

Near La Purisima the Comondu Formation 1s over-
lain by 12—6 Ma Late Miocene plateau basalts such as
the thick flow capping El Pilon in Arroyo la Purisima
(Text-fig. 22), and by unnamed canyon-fill lavas show-
ing reverse topography in the type area, youngest lavas
in the canyon floors and oldest basalts toward the top
(Text-fig. 23). These are in turn overlain by young cin-
der cones of 0.4—0.9 Ma (McLean and Hausback,
1984).

West of Loreto, near Cerro de las Parras, McLean
(1988) mapped ‘volcaniclastic rock” along the road
to San Javier. Regarded informally by many as the
Comondu Formation, these rocks are intruded by a
hornblende andesite porphyry with a K/Ar age of 19.4
+ 0.9 Ma (McLean er al., 1987). This and other ages

44 BULLETIN 371

of underlying and intrusive rocks constrain the sedi-
ments in this area to approximately 18-22 Ma, con-
siderably older than the type section of the Comondu
Formation (McLean, 1988).

Differing concepts of the Comondu Formation.—No
other lithologic unit in the Baja California peninsula
has been so broadly interpreted. The name **Comon-
du’ has been used for Oligocene to Pliocene volcanic
tuffs, flows, and volcaniclastic rocks from Santa Ros-
alia to San Juan de la Costa, the La Paz peninsula, and
the Cabo Trough. Many workers, beginning with Beal
(1948), included volcanic rocks in the Comondu For-
mation or the Comondu Group without regard for the
sedimentary nature of the type section. I. EF Wilson
(1948), I. F Wilson and V. S. Rocha (1955), and Mina-
Uhink (1957) used Comondu Formation for volcanic
rocks as far north as Santa Rosalia. Sawlan and J. G.
Smith (1984) and Sawlan (1991) discussed differences
between true volcanic are rocks from the Sierra Santa
Lucia (between Santa Rosalia and Mulege) and the
arc-derived sediments at the type locality at San José
de Comondu.

Using the definition of a formation in the North
American Stratigraphic Code (1983), the Comondu
Formation would be restricted to the largely coarse
clastic sedimentary unit in its type area in the Sierra
la Giganta and finer-grained facies in parts of the west-
ern embayment. Derived from older are volcanic rocks
in the area of the present Gulf of California, it is not
itself an arc volcanic rock (Sawlan and J. G. Smith,
1984). Its only volcanic components are several minor
tuffs and flows in sections north of Arroyo la Purtsima
(McLean er al., 1987). Younger plateau and canyon-
filling basalts in the type area are related to later epi-
sodes of volcanism, not arc volcanism; they are not
part of the Comondu Formation.

Our concept of the unit contrasts with those of
Hausback (1984a,b) and later workers, who include in
the Comondu Formation wide bands of volcanic and
volcaniclastic rocks from the Concepcion Peninsula
and the Loreto basin as well as multiple ash-flow tufts
near San Juan de la Costa and La Paz. Those tuffs
range in age from 22—12.5 Ma, most between 17 and
22 Ma. By this definition, the Comondu Formation
would include both arc and non-are lithologies of dif-
ferent provenances and an age spanning at least 10
million years.

McFall (1968) regarded his older units on the Con-
cepcion Peninsula as the Comondu Group (p. 81). His
section includes basalts, tuffs, conglomerates, sand-
stones, and agglomerates that range in age from 30—
17 Ma, Late Oligocene to Early Miocene, significantly
older than the Comondt Formation in its type area.

We prefer the descriptive terms “unnamed volcan-
iclastic rocks, near-vent facies or distal vent facies,”
following McLean (1987), for sediments derived from
the Miocene volcanic are that lay east of the present
Loreto basin between 24 and 11 Ma (Sawlan, 1991).
J. G. Smith (1993) provided a concise discussion of
the nature and nomenclature of volcanic and volcani-
clastic rocks that are formed, deposited, and reworked
in a subaerial are environment. He favors a more in-
terpretive terminology based on composition, age, and
facies, as used by McLean (1988) and McLean et al.
(1987), rather than conventional stratigraphic units
such as formations or Groups.

Proximal volcanic arc facies mapped as ““Comondu
Formation.’’—“Comondu” has been used in unpub-
lished reports and primarily paleontological papers on
the sections at Loreto, Arroyo San Carlos, Punta San
Telmo, and Tembabiche, and for the upper, nonmarine
volcanic and sedimentary units at San Juan de la Cos-
ta. Measured sections from Tembabiche show volcan-
iclastic sandstone and breccia overlying the El Cien
Formation as subunits of the Comondu Formation
(Plata-Hernandez, 2002; Plata-Hernandez and
Schwennicke, 2000). Our columns refer to these as
unnamed volcaniclastic sediments, pending the further
mapping and analysis underway in the Tembabiche

area.

Cuesta Formation, obsolete name.—Heim (1922)
introduced the name Cuesta Formation for unfossilif-
erous gray sandstones overlying the Comondu_ For-
mation and forming the rim of the mesa near La Pur-
isima. Later mappers included them in the Isidro For-
mation.

Plateau basalts, capping volcanic rocks, canyon-fill
lavas and cinder cones.—Younger volcanic rocks that
overlie the Comondu Formation in the western Sierra
la Giganta are locally-derived, separate, unnamed an-
desite and basalt flows 14-11 Ma and 7 or 8 Ma in
age (McLean er al., 1987). Quaternary cinder cones
and canyon-filling flows are as young as 0.40 to 0.9
Ma. El Pilon, a well known example of an erosional
remnant in Arroyo la Purisima, is capped by a younger
basalt flow (Text-fig. 22).

Magdalena embayment, southern part of
the Western embayment
Plate 1, Columns 17, 18, 19
(Text-figs. 2, 24-34, Table 5, Appendices 1, 2)

Overview

The Magdalena embayment contains Late Creta-
ceous to Late Miocene or Early Pliocene marine sed-
iments that extend 400 km (250 mi) from north of

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 4

Table 5.—Western Magdalena embayment, lithostratigraphic units (Text-figs. 28, 33). Lowercase names indicate informal units that were

not established according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Cerro Colorado Mem-

ber

Cerro Tierra Blanca

Member

El Cien Formation

Salada Formation

San Hilario Member

San Juan Member

Tepetate Formation

Applegate (1986) named as up-

per member of El Cien Forma-
tion.

Applegate (1986) named as low-

est member of El Cien Forma-
tion. Fischer ef al. (1995) re-
garded as lower part of their
San Juan Member.

Applegate (1986) named the for-

mation and three members:
Cerro Tierra Blanca, San Hi-
lario, and Cerro Colorado.
Fischer et al. (1995) proposed
the San Juan Member as an
alternative for Applegate’s two
lower members.

Heim (1922). Schwennicke

(1998) relocated and remea-
sured the type section.

Applegate (1986) named as the

middle member of the El Cien
Formation. Fischer er al.
(1995) included in their San
Juan Member. Hausback
(1984b) mapped as San Gre-
gorio Formation.

Fischer et al. (1995) named as

lower part of El Cien Forma-
tion, after Schwennicke (1992,
1994). These authors regarded
the Cerro Tierra Blanca and
San Hilario Members of Ap-
plegate (1986) as the San Juan
Member.

Heim (1922). Fulwider (1976,

1984) distinguished three sub-
units in Arroyo Colorado, old-
est to youngest: Cannonball
member, interbedded claystone
and siltstone member, and a
crossbedded member.

Member includes sandstone, siltstone, tuffaceous sandstone, conglom-
erate, and porcellanite. It is nonmarine at its type section on the
west side of Cerro Colorado, approximately 5 km east of Las Poci-
tas in the quadrangle of the same name. In other locations the
member varies from marine to lagoonal or nonmarine (Gidde,
1992a). Early Miocene, older than 21.0 + 0.4 Ma, the date of an
ash-flow tuff in the overlying voleaniclastic sediments south of San
Juan de la Costa (Hausback. 1984b).

Member has a basal marine conglomerate with abundant shark teeth
and reworked turritellid fragments overlain by microfossiliferous
sandstone and tuffaceous siltstone with calcareous concretions.
Type section is on the west side of Cerro Tierra Blanca, which ad-
joins the southwestern side of Cerro Colorado, Las Pocitas quad-
rangle. Locally its upper boundary is marked by resistant flag
stones, the Llajas Palo Verde of Ojeda-Rivera (1979). Late Oligo-
cene—Early Miocene (Carreno, 1992b).

Formation includes marine and nonmarine clastic sediments with mi-
nor tuff beds that overlie the Tepetate Formation with angular un-
conformity. Type section is approximately 125 m thick, the most
complete sequence of the outcrop areas (Fischer ef a/., 1995); it 1s
a predominantly marine sequence that is exposed on the west flank
of Cerro Colorado, northeast of Pénjamo, and in the walls of Ar-
royo San Hilario east of El Cien (km 100), Las Pocitas and San
Juan de la Costa quadrangles, respectively. Late Oligocene—Early
Miocene, based on fossils and interbedded and overlying radiomet-
rically dated volcanic rocks (Hausback, 1984b).

Unit has fossiliferous, shallow-water, marine and nonmarine facies
that include sandstone, agglomerate, and coquina described from
the southeast side of Arroyo la Salada below the site of Rancho la
Salada (GPS coordinates for site are 24°29.797' N, 111°32.137' W).
Type section extends 600 m along the arroyo at the southern edge
of the Santa Rita quadrangle. Originally considered Pliocene, but
more recent studies suggest a Late Middle to early Late Miocene
age (Smith, 1992; L. G. Barnes, 1995).

Member consists of fossiliferous marine sandstone and tuffaceous,
phosphatic and diatomaceous facies exposed in cliffs along Arroyo
San Hilario. Applegate’s type section was described from the area
of Rancho San Hilario, east of El Cien, San Juan de la Costa quad-
rangle. Late Oligocene—Early Miocene?, based on a rhyolite tuff
with a K-Ar age of 25.5 + 0.4 Ma near the top of the section in
Arroyo San Hilario (Hausback, 1984b).

Member includes fossiliferous marine sandstone, conglomerate, fan-
glomerate, tuffaceous, and phosphatic facies, and the phosphorite
layers (“capas’’) that were mined at San Juan de la Costa. Com-
posite type section is exposed east of El Cien along parallel limbs
of a syncline. The western outcrops are near Rancho el Agujito de
Castro, El Conejo quadrangle; the eastern beds crop out in Arroyo
Amarga, 4+ km northwest of San Juan de la Costa, San Juan de la
Costa quadrangle. Oligocene.

Formation is a marine unit that includes soft greenish sandstone, well-
stratified gray sandstone, and claystone with abundant discocyclinid
foraminifers. Type section in the bottom of Arroyo Colorado is
west of Mexico | and |—2 km southwest of Rancho Tepetate, Las
Pocitas quadrangle. Formation originally regarded as Late Creta-
ceous to Eocene, but later workers suggest Late Paleocene to early
Middle Eocene (Carreno ef al., 2000).

46 BULLETIN 371

Ciudad Constitucion to south of Arroyo el Conejo; iso-
lated Miocene outcrops are present as far south as Ar-
royo la Muela, near Todos Santos.

In the Late Oligocene, the Magdalena embayment
extended from the east coast of the present Baja Cal-
ifornia peninsula to the Pacific Ocean, as seen from
near-shore deposits from Arroyo San Carlos and Punta
San Telmo to San Juan de la Costa (p. 92). Facies and
depth changes during the Oligocene complicate cor-
relation between those units and the type section of
the El Cien Formation at Cerro Colorado and Arroyo
San Hilario, north and east of El Cien (Text-fig. 33).

The Magdalena embayment is the southern part of
a series of western embayments that existed as far
north as Laguna San Ignacio and included the western
slopes of the Sierra la Giganta between Arroyo Mez-
quital and Arroyo la Purisima (Text-fig. 2). Paleogene
and early Neogene marine deposition occurred while
the Baja California peninsula lay against mainland
Mexico, when the western Magdalena area was the
next embayment north of the La Mira basin of Nayarit
and Michoacan (Text-fig. 35d,e herein; Durham et al.,
1981; Perrilliat, 1987, 1992; J. T. Smith, 1991c).

Reconnaissance maps of the area assign a number
of different names to the stratigraphic units (see sum-
maries by Applegate, 1986; Carreno, 1992b; Fischer
et al., 1995). Further mapping and detailed analyses
are needed to refine interpretations of formations,
members, facies, contacts, and correlation. The revised
age of the type Salada Formation, from the Pliocene
of early workers to Middle to early Late Miocene, has
important implications for the geologic history of the
region (J. T. Smith, 1992). Marine fossils from hard
gray sandstone clasts in the lower part of the Salada
Formation are key to correlating sediments in the Pur-
isima-Iray basin and the Magdalena embayment.

Granitic and metamorphic basement rocks are not
exposed in the onshore western Magdalena embay-
ment, although Mesozoic (?) rocks of oceanic origin
crop out on Isla Margarita and Isla Magdalena (For-
man er al., 1971; Rangin and Carrillo-Martinez, 1978;
M. C. Blake er al., 1984). Sedlock (1993) interpreted
these rocks as parts of volcanic arcs and ophiolitic ter-
ranes that were accreted to the Baja California penin-
sula in Late Jurassic or earliest Cretaceous time.

El Rifle

Arroyo Salada—Santa Rita
Plate 1, Column 17
(Text-figs. 1, 24-30, Table 5, Appendices 1, 2)

Column modified from Heim (1922), Fulwider
(1976), and Schwennicke (1998). Area is shown on
the Santa Rita quadrangle, G12C68, Puerto Chale
quadrangle, G12C78, and Las Pocitas quadrangle,
G12C79, 1:50,000. Beal (1948) and Mina-Uhink

(1956, 1957) published geologic maps that included
the area.

Stratigraphy

Tepetate Formation, latest Cretaceous to Early Eo-
cene.—The Tepetate Formation crops out from Arroyo
Salada to Arroyo el Conejo, approximately 75 km
north of La Paz on Mexico 1, and as far east as Cerro
Colorado (Fulwider, 1976; Galli-Olivier et al., 1986;
Squires and Demetrion, 1991) (Text-figs. 28, 30).

Fulwider (1976, 1984, 1991) discussed sections in
Arroyo Salada, where he recognized only the two old-
er informal subunits of the type area, the massive, un-
fossiliferous Cannonball Sandstone and an interbedded
claystone and siltstone. They crop out near Rancho el
Médano and Rancho el Sauce, where the unit dips 20°
to the northeast. He regarded the lowest beds as Late
Cretaceous to Eocene in age, based on microfossils.
The base is not exposed; the upper contact with the
Salada Formation is unconformable.

Salada Formation, late Middle to early Late Mio-
cene.—Heim (1922) described the Salada Formation
while staying at Rancho la Salada in 1915. Then a
thriving cattle ranch, it is now difficult to find the few
green mezquite trees and scattered bricks that represent
the original site 30 m from the edge of the plateau
(Text-figs. 24, 25, 26). The access ramp has crumbled
away; a sketch from Gabb’s early traverse showed it
800—1,000 m north of a ranch building (Browne, 1868,
p. 12). Schwennicke (1998) relocated the site 10-15
km southwest of Santa Rita, and the type section in
the arroyo below. He provided GPS coordinates for
the ruins: 24°29.889' N, 111°31.907' W (Schwennicke,
personal communication, 2003).

Field notes in the Smithsonian Institution’s National
Museum of Natural History and fossils collected by
Heim and later Darton confirm Schwennicke’s (1998)
report of the type section downstream from Rancho
Agua Verde and I—1.5 km upstream from the section
near the ruins of a World War II adobe fort (Text-fig.
28).

Heim (1922: 544—546) published a detailed descrip-
tion of the type section; A, its upstream end, has GPS
coordinates 24°30.153' N, 111°31.573' W (Schwen-
nicke, oral communication, 2003). He described fine-
and coarse-grained sandstone and coquina beds ex-
posed for 600 m along the southeastern wall of the
arroyo and dipping a few degrees to the west (Text-
figs. 24, 25, 28). He designated the lowest facies as
Bed 1, the uppermost unit as Bed 10. Bed 9, his
“Great Pecten bed,” contains a Tertiary-Caribbean
pectinid identified by J. T. Smith (1992) as Chlamys
sp. cf. C. tamiamiensis (Mansfield) subsp. Unconform-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 47

able Pleistocene marine terrace deposits (Heim’s Bed
11) cap the section.

Schwennicke (1998) and Schwennicke er al. (2000)
measured 14 m of section along A—B at the base of
the cliff. They refined descriptions of Heim’s ten beds,
including a basal lagoonal, phosphatic facies at water
level overlain by a key fossiliferous marine conglom-
erate (Bed 2) and fossiliferous sandstone (Bed 3). They
verified differences between the section at A and the
facies at B, which include a 2- to 3-m-thick lens of
reworked coquina, Schwennicke’s Bed 3a (Text-fig.
25). They noted large, unfossiliferous, well-indurated
clasts at low-water level, at the boundary between the
Bed 2 conglomerate and the sandstones of Bed 3.
Schwennicke (1998) also identified a number of fluvial
facies within the marine sediments and related the type
section to measured sections at El Médano.

A number of workers in the 1980s and 1990 made
reconnaissance visits to the area of the old adobe fort,
believing it was the type section. A deteriorating stony
ramp north of the fort provided access to the arroyo
and the section of the Salada Formation. On several
visits they observed well-indurated gray sandstone
clasts bearing molds of large pectinids and other fos-
sils, the “basal concretionary layer” of Smith (1992).
The clasts weather from beds that are exposed inter-
mittently at low water level between the ramp and 50
m upstream; at times they are buried by river mud
(Text-fig. 27). The locality is shown on Text-figure 28
as 03JS4 (= 89JS3 = 83JS22). Its GPS coordinates
are 24°29.797' N, 111°32.137' W.

Regarded as the lowermost bed of the Salada For-
mation by Smith (1992), the unit was reassessed by
Schwennicke and Smith in 2003 as a marine facies of
the well-indurated sandstone whose clasts mark the
contact between Beds 2 and 3 at the type section. The
clasts contain molds of the giant pectinids Euvola sp.,
Amussiopecten sp., Amusium sp., Flabellipecten sp.,
and external molds of Chlamys sp. cf. C. tamiamiensis
(Mansfield) subsp. (Text-figs. 27, 29). Preliminary tax-
onomic studies suggest Amussiopecten sp. and Amu-
sium sp. are the same as Isidro Formation species; the
chlamyd occurs in concretions between Beds 2 and 3,
in Heim’s Bed 9 of the type section, and in Miocene
marine rocks of the Paraguana Peninsula, Venezuela.

The Salada Formation was deposited on an irregular
surface in the Magdalena embayment. It overlies the
Tepetate Formation with angular unconformity near
Rancho el Médano, where the contact is marked by
prominent, bulbous burrows in the Tepetate Formation
filled with Salada Formation sandstone and fossils.
Schwennicke and Gonzalez-Barba (1995) regarded the
Salada Formation there as equivalent to Heim’s type
section Bed 2. Schwennicke er al. (2000) reported that

its easternmost outcrops near Microondas El Rifle (km
135) are also penecontemporaneous with the type sec-
tion. The unit is exposed from Arroyo la Salada to
Rancho el Conejo, and intermittently as far south as
Arroyo la Muela north of Todos Santos (Text-figs. 30,
73).

To the north the Salada Formation was reported
from wells such as Pozo Iray #2 near Puerto Adolfo
Lopez Mateos (Text-figs. 30, 56 herein: Mina-Uhink,
1957) and at the mouths of *... every river bed near
the Pacific coast” from La Poza Grande to Arroyo San
Gregorio (Heim, 1922). Heim’s figure 6 shows out-
crops near the mouth of Arroyo Cadegomo [= Arroyo
la Purtsima], where he reported the same fossils, 1n-
cluding bryozoan-encrusted gastropods, that occur in
Arroyo la Salada. He questioned whether fossiliferous
marine agglomerates at La Ventana were also a facies
of the Salada Formation.

Although Mina-Uhink (1957) mapped the Salada
Formation in the valle central of Isla Margarita, off-
shore from Bahia Almejas, the geologic map of Ran-
gin and Carrillo-Martinez (1978) and reconnaissance
field work in 1985 by J. T. Smith, J. R. Ashby, Jr., G.
Padilla-Arredondo and S. Pedrin-Avilés found only
Quaternary sands. The unit is not present on Isla Mag-
dalena, but marine fossils were observed north of the
lighthouse at Cabo San Lazaro in outcrops on the north
side of a circular cove (J. A. Minch, written commu-
nication, 2002).

Age of the Salada Formation, Late Middle to early
Late Miocene.—Although the Salada Formation was
regarded as Pliocene by Heim (1922), Beal (1948), and
Mina-Uhink (1957), radiometric data and marine fos-
sils indicate it is Late Middle to early Late Miocene
(J. T. Smith, 1992, and ongoing research).

A Middle Miocene (14 Ma) to Late Miocene (6 Ma)
age, depending on which seawater strontium ratio
curves are used to interpret the data, was determined
by R. E. Denison, then of Mobil Oil Company. He
reported a Miocene age for a pectinid collected from
Heim’s Bed 9, several meters below the Pleistocene
terrace deposits that cap the type section (Text-fig. 28,
fossil locality 83JS23, herein; R. E. Denison, written
communication, 1991). The dated pectinid was Mobil
Oil Corporation sample 8517 with a *’Sr/*°Sr value of
0.708870 + .000026, A,,, = —20.3.

Vertebrates reported from the Salada Formation in-
clude Miocene sea lions, walruses, pinnipeds (Barnes,
1995, and oral communication), and Pliocene and
Miocene sharks (Ashby, 1987; Schwennicke and Gon-
zalez-Barba, 1995). Miocene age-diagnostic marine bi-
valves such as Clementia dariena (Conrad), Raeta gib-
bosa (Gabb), Cyathodonta gatunensis (Toula), and Le-

48 BULLETIN 371

Rancho site

* El Médano BN

\ ‘il psasco }
id) I =
eres “i | ees
—_—_ uy |
0 2KM 3 h
a SE
— > }:
= Hf
ee ie
\>
S éLa Calera
° i
oe: fa 5 if
\ a Ya Agua Verde
. v !
Py !
, Cementerio ;
A. | Santa Rita quadrangle
23
ae ene Vea 382 eee 24° 30'N
Rancho Salada (ruins)” ate 5
‘ @"83IS22, 03584 , 7, Puerto Chale quadrangle
a 2) old fort (ruins) “|
/ ‘@ Rancho
{ © =Town/village
he Unpaved road
® Megafossil locality

Fs Salada type section

a *7Sr/8Sr age locality
Valley edge
111° 30'W

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 49

porimetis trinitaria (Dall) are Tertiary-Caribbean taxa.
Gastropods, shells encrusted by the bryozoan Anto-
pora tincta (Hastings), and elongate balanid barnacles
are also present in the fauna (J. T. Smith, 1992; P. A.
Morris and J. T. Smith, 1995).

Correlation

The Salada Formation has been used broadly for
rocks of varying lithology, provenance, and age over
much of the Baja California peninsula. The name has
been applied to areas as distant as the Sierra San Felipe
in the northern Gulf of California and the southern San
José del Cabo Trough, for any yellow sandstone with
“Pliocene marine fossils,” based on the age given by
Heim (1922). Mollusks, vertebrates, and strontium iso-
tope data from the type area indicate a significantly
older unit that 1s not correlative with Pliocene sections
in the ancient Gulf of California (J. T. Smith, 1992;
Schwennicke and Gonzalez-Barba, 1995; Barnes,
1995, and oral communication, 2000).

Mapping is needed to determine overlap between
the Salada Formation and the upper Isidro Formation.
The Salada Formation at Arroyo la Muela could be
older than the type section (Schwennicke ef al., 2000).
Molluscan taxa from the Salada Formation also occur
in the Gatun Formation of Panama, the Tubera For-
mation of Colombia, the Cantaure and Paraguana For-
mations of Venezuela, the Gurabo Formation of the

Dominican Republic, and the Springvale Formation of

Trinidad (J. T. Smith, 1992).

Salada Formation at El Rifle, Late Miocene to Early
Pliocene.—The Salada Formation near Microondas El
Rifle (km 135) is 4—5 m thick and could be penecon-
temporaneous with the type section Schwennicke ef al.
(2000). Shark teeth suggest an Early Pliocene age (Es-
pinosa-Arrubarrena and Applegate, 1981). The Salada
Formation is overlain unconformably by latest Pleis-
tocene lake deposits containing Rancholabrean Stage

freshwater turtles and algal stromatolites (E. C. Wil-
son, oral communication, 1989; Ferrusquia-Villafranca
and Torres-Roldan, 1980).

Quaternary terrace deposits.—Highly fossiliferous
marine terrace deposits on Isla Margarita at Puerto Al-
catraz, east of Puerto Cortés, were dated at 120,000
years (Wehmiller and Emerson, 1980). Fossiliferous
Pleistocene terrace deposits also occur at Punta Bel-
cher, Isla Magdalena (Jordan, 1936).

El Cien
Plate 1, Column 18
(Text-figs. 30—35, Table 5, Appendices 1, 2)

Columns modified from Carreno (1992b), Schwen-
nicke ef al. (1996), Schwennicke and Plata-Hernandez
(1997), and Fischer et al. (1995). Area 1s shown on
Las Pocitas quadrangle, G12C79, La Fortuna del Bajio
quadrangle, GI2C69, and El Conejo quadrangle,
G12D81, scale 1:50,000; the locality maps of Fischer
et al. (1995); and the geologic maps of Mina-Uhink
(1957), Hausback (1984a,b), and Carreno (1992b).

Overview

Oligocene to Miocene marine units crop out in the
Magdalena Plain between Rancho San Luis Gonzaga,
southeast of Ciudad Constitucion (km 212), and Ran-
cho el Aguajito de Castro, near km 70—74 on Mexico
| (Text-figs. 30, 56). These sediments overlie the ma-
rine Tepetate Formation, which was deposited during
multiple transgressive-regressive cycles.

Visited by Heim in 1915, Darton in 1920 and Mina-
Uhink in 1943, the northern Magdalena Plain from
Rancho la Fortuna to Rancho San Luis Gonzaga has
not been remapped in recent times. Detailed studies of
those outcrops are needed to assess and relate the
members of the El Cien Formation of Applegate
(1986) and the more recently introduced San Juan
Member of Schwennicke (1994, 1995) and Fischer et

Text-figure 24.—Arroyo La Salada and the Magdalena Plain, view southwest at Heim’s type section (A-B) and mezquite trees that mark

the site of Rancho La Salada on the Pleistocene terrace. Photo, Tobias Schwennicke, 1996.

Text-figure 25.

Salada Formation at B, southwestern end of type section. Well-indurated, unfossiliferous concretions in the stream bed

weathered out of Heim’s Bed 2. The highly fossiliferous, prominent 2—3-m-thick resistant coquina is Heim’s Bed 3 = Bed 3A of Schwennicke

(1998). Photo, Tobias Schwennicke, 1995.

Text-figure 26.—Tobias Schwennicke surveys scattered bricks that remain from Rancho La Salada. Gabb camped here in 1867, Heim stayed

in 1915, and Darton visited in 1921. Photo, J. T. Smith, 2003.

Text-figure 27.—Fossiliferous clast of well-indurated gray sandstone in Arroyo La Salada, upstream from the site of an old fort. The adobe

walls of the World War II fort were reduced to less than 20 cm by 2003. In the arroyo, 1—1.5 km downstream from the type section, concretions
marking the contact between Heim’s Bed 2 conglomerate and Bed 3 sandstone contain giant pectinids (J. T. Smith megafossil localities 83JS22

= 89JS3 = 03JS04). Photo, J. T. Smith, 1985.

Text-figure 28.

Salada Formation, map of type area south of Santa Rita and El] Medano. A—B, type section, Beds |—9 of Heim (1922);

“’Sr/°Sr date at 83JS23 determined on a pectinid from Heim’s Bed 9 is in the range of Middle to Late Miocene.

50 BULLETIN 371

Text-figure 29.—Giant pectinid molds from the contact between

Heim’s beds 2 and 3 at the old fort section. The right valve at lower
left could be the largest individual recorded for the genus Amussi-
opecten (Los Angeles County Museum of Invertebrate Paleontology
hypotype 7632); the other right valve is Euvola sp. (Los Angeles
County Museum of Invertebrate Paleontology hypotype 7633). J. T.
Smith locality 89JS3 = O3JS04 of Text-figure 28. Photo, J. T. Smith,
1985.

al. (1995). Biofacies studies of the Cerro Colorado
Member, the upper subunit of the El Cien Formation,
by Gidde (1992a,b and in Fischer et al., 1995) indicate
it contains both marine and nonmarine facies, regress-
ing upsection to a continental deposit. Earlier literature
refers the Oligocene—Miocene marine sequences in
this area to older names, including the San Gregorio
and Isidro Formations, which were described from the
Purisima-Iray basin to the north. Table 5 summarizes
the stratigraphic nomenclature, which ts still under dis-
cussion.

Granitic and metamorphic basement rocks do not
crop out in the western Magdalena embayment.

Stratigraphy

Tepetate Formation, late Early Eocene to early
Middle Eocene.—The type area in Arroyo Colorado
was revisited by Carreno er al. (2000), who reviewed
its stratigraphy, age, and depositional history. Strata in
Arroyo Colorado were not designated by Heim (1922)
but were regarded as the stratotype by Mina-Uhink
(1957); the section has GPS coordinates 24°23'17.7"
N, 111°07'53.2” W (Instituto de Geologia Museo de
Paleontologia locality IGM-2984).

Carreno ef al. (2000) divided the northeast-dipping
55-m-thick section into seven lithological units sepa-
rated by erosional contacts; they recommended using
a composite stratotype to represent the lithologic var-

iation and longer chronostratigraphic range of the unit
as a Whole. The base is not exposed and the lowest
part has no diagnostic planktonic foraminifers. Micro-
fossils from the unit as a whole suggest outer shelf to
upper bathyal depths (Carreno ef al., 2000). In the El
Cien area the upper contact with the Late Oligocene
Cerro Tierra Blanca Member is an angular unconfor-
mity: in Arroyo Salada the overlying unconformable
unit is the Miocene Salada Formation.

Fulwider (1976, 1984, 1991) recognized three in-
formal subunits of the Tepetate Formation in Arroyo
Colorado and characterized them as follows. The old-
est is the massive, unfossiliferous, Cannonball sand-
stone with 0.5-m-diameter concretions. The middle in-
terbedded claystone has chocolate-colored upper sed-
iments and purplish lower ones, sandy siltstone lenses,
and calcarenite beds; its most recognizable facies is
the foraminiferal siltstone in the upper part that con-
sists largely of the discocyclinid identified as Pseu-
dophragmina (P.) advena Cushman by Carreno et al.
(2000) and as Pseudophragmina (P.) cloptoni
(Vaughan) by earlier workers, including Knappe
(1974) and Pulwider (1976). The cross-bedded mem-
ber, youngest in the sequence, has alternating silt-
stones, sandstones, and silty-claystone layers that are
exposed only in the Arroyo Colorado area. Fulwider’s
range of Cretaceous to Paleocene for the lower part of
the section was based on microfossils.

Perrilliat (1996), sampling a different facies approx-
imately 2 km southwest of El Cien, reported shallow-
water tropical mollusks, including the Old World Teth-
yan gastropod genera Campanile and Gisortia, and as-
sociated late Early Eocene foraminifers (Carreno in
Perrilliat, 1996).

The Tepetate Formation is mapped from Arroyo la
Salada to Arroyo el Conejo, which is 75 km north of
La Paz on Mexico | (Galli-Olivier er a/., 1986; Squires
and Demetrion, 1991). Although it was reported in pa-
pers on the geology of San Juan de la Costa, we agree
with Mina-Uhink (1957) that outcrops are restricted to
the western Magdalena embayment.

Age and Correlation, Early Eocene to early Middle
Eocene.—The type section contains planktonic fora-
minifers ranging from the latest Lower Eocene Acar-
inina pentacamerata Zone to the earliest Middle Eo-
cene Hantkenina nuttalli Zone, equivalent to the Pe-
nutian to Narizian benthic foraminiferal stages of Cal-
ifornia (Almgren ef al., 1988). Its latest Early Eocene
to early Middle Eocene age (51.2—48.4 Ma) is based
on 54 species of benthic and planktonic foraminifers;
Carreno et al. (2000) regarded poorly preserved Cre-
taceous or Paleogene taxa as reworked.

Fulwider (1976, 1984, 1991) reported a latest Cre-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH a1

taceous to Early Eocene age for the formation as a
whole, with the section near Rancho el Sauce in Ar-
royo la Salada older than the type section. Vazquez-
Garcia (1996) identified middle Late Paleocene to Ear-
ly Eocene planktonic foraminifers from the Tepetate
Formation in Arroyo el Conejo (Carreno et al., 2000).
Parts of the Tepetate Formation are coeval with parts
of the Bateque Formation to the north. The lower part
of the Tepetate Formation at Arroyo Colorado corre-
lates with the middle Early Eocene age, ““Capay” Pro-
vincial Molluscan Stage facies of the lower Bateque
Formation at its type area (Squires and Demetrion,
1991). Both formations contain distinctive discocyclin-
id facies and abundant megafossils, including mol-
lusks, corals, calcareous sponges, and echinoids.

El Cien Formation, Late Oligocene to Early Mio-
cene.—The El Cien Formation was named by Apple-
gate (1986) for marine to continental clastic deposits
near El Cien (km 100) and east of the Mexico 1 at
Cerro Colorado and Arroyo San Hilario (Text-figs. 31—
33). Darton (1921) referred to these units as the **Yel-
low beds” and the Monterey Formation. Mina-Uhink
(1957) mapped them as the Monterrey and Isidro For-
mations. Hausback (1984a,b) and Kim (1987) regarded
the rocks between El Cien and San Juan de la Costa
as the San Gregorio and Isidro Formations, names that
are used in the Purisima-Iray basin. Early stratigraphic
terminology was reviewed by Applegate (1986), Car-
reno (1992b), and Fischer ef a/. (1995), among others.

Paleontological, stratigraphic, and radiometric data
indicate a Late Oligocene to Early Miocene age, 27
Ma to 17 Ma (Carreno er al., 1997), for lithofacies that
include sandstone, siliceous shale, limestone, porcel-
lanite, tuff, and conglomerate. The formation crops out
over much of the eastern and central Magdalena em-
bayment, from Rancho San Luis Gonzaga, Rancho el
Platano and La Presa, north of Rancho la Fortuna, to
north of the Aguajito Fault in the El] Conejo quadran-
gle. It is mapped along the Gulf of California between
Arroyo San Carlos and San Juan de la Costa (Carreno,
1992b). Text-figures 35d,e show the paleogeography
of the Magdalena embayment at the time the El Cien
Formation was deposited.

Applegate (1986) also named three members in the
El Cien Formation, from oldest to youngest: Cerro Ti-
erra Blanca, San Hilario and Cerro Colorado. Fischer
et al. (1995) proposed an alternate interpretation based
on sections near San Juan de la Costa and Rancho el
Aguajito de Castro. They recognized only two subdi-
visions, the older San Juan and younger Cerro Colo-
rado Members.

Cerro Tierra Blanca Member of Applegate (1986),
Late Oligocene to Early Miocene.—The unconformity

between the basal pebble conglomerate of the Cerro
Tierra Blanca Member and the underlying Tepetate
Formation can be seen along Mexico | at km I11 and
on the western flanks of Cerro Tierra Blanca. The unit
contains diatoms, planktonic foraminifera, and a large
number of shark species, including Carcharodon so-
kolowi (Jaeckel) (Applegate, written communication,
1991), that indicate a Late Oligocene to Early Miocene
age (Carreno ef al., 1997). Pectinids and _ turritellid
fragments from this horizon are under investigation.

Schwennicke (1992) measured another section of
mudstone, tuff, and phosphorite beds at Cerro Colo-
rado; he reported that the local horizon known as Lajas
Palo Verde of Ojeda-Rivera (1979) does not extend to
Arroyo Aguayito and other drainages. He interpreted
this and the following unit as the San Juan Member.
Text-figure 33 shows the type and study areas of the
El Cien Formation and its members.

San Hilario Member of Applegate (1986), latest Ol-
igocene to Early Miocene.—The San Hilario Member
has many facies, including phosphatic and diatoma-
ceous marine sandstones, a widespread horizon of the
bivalve Anadara vanderhoofi Durham, and an upper
massive sandstone. Hausback (1984b) dated a Late Ol-
igocene rhyolite tuff near the top of the section at Ar-
royo San Hilario (Text-fig. 32); a green porcellanite
marks the upper contact with the overlying Cerro Col-
orado Member.

Kim (1987) studied well-preserved planktonic for-
aminifers from Arroyo San Hilario and assigned the
beds to Planktonic Foraminiferal Zones P21 and P22
(31.6—24.4 Ma) of Berggren er al. (1985). Kim (1987)
and Kim and Barron (1986) referred sections in this
area to the San Gregorio and Isidro Formations, most
of which fall within Applegate’s San Hilario Member.
They identified Early to Late Oligocene tropical dia-
tom zones in the two lower members of Applegate,
and recognized a mixture of tropical and cool water
species that indicate a high rate of upwelling. Their
data also suggest that the cool water California Current
was already influencing the Magdalena embayment in
Oligocene time.

Correlation

Beds at the mouth of Arroyo San Carlos and to the
south contain abundant specimens of Anadara van-
derhoofi Durham that also mark the top of the type
section east of El Cien (Applegate and Wilson, 1976:
Carreno, 1992b). Diatom zones are the same in several
formations in the Magdalena embayment and the Pur-
isima-Iray basin, but correlation is complicated by fa-
cies changes and_ stratigraphic terminology (Kim,
1987; Kim and Barron, 1986).

BULLETIN 371

Villa Insurgentes

Ciudad Constitucién
-@ San Luis Gonzaga
E| Platano

/
San Juan

de la Costa

= )
= WAY
nto
‘i
0 8 16KM of:
—— !17o Ww
@ Rancho
Pe Arroyo Mexico highway 1
Pozo/well ~~ Unpaved road
Town/village Old road from Loreto to La Paz
Microwave tower Area of Text-fig. 28
| aa Ti? 00° W 110° i; 74
i a3 «! - moans S 45'W / 45'N
».\8 jo Ao at ) Punta
Kon W\GO 2 0 wg Coyote
@ LZ NS Co
t—-s La Fortuna: EN o
o/ RS =
ie / v °
wot ry . 2
} a CE eer SIR
J La Matanza \G y ~Caiiada de la Luz =
oY as STDs | =
Ss me EI Pilar Naat 7 =
_ Tarabillas~' S
os t Punta el
Begs eg B Junco
| @& Amarega | =
ar San J
e San Juan
a de la Costa
3 | ae J
A. Aguajito 240 I ae
O'-7
w/ ot “| |
a) —— ae ate Aguajito de Castro
Oc > =~ ee
Co %e. ~ S/
| % eae hay y
&
Ny N
@ Rancho Oy) Mexico highway | j
e =©Town/village & Microfossil locality
Unpaved road @ Megafossil locality _
s& Cerro/Hill Ua

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

Cerro Colorado Member, late Early Miocene to
Middle Miocene.—The Cerro Colorado Member is a
regressive sequence of sandstones, tuffaceous sand-
stones, and conglomerates. It is nonmarine at its type
section and some areas east of Rancho la Fortuna,
where it contains root casts. Elsewhere it consists of
fossiliferous shallow-water marine facies (Gidde,
1992; Gidde in Fischer et al., 1995). Reworked silic-
ified wood fragments from mainland Mexico occur in
extensive beds at Rancho Matanzas, 22 km north of
Cerro Colorado (Applegate, 1986; Cevallos-Ferriz and
Barajas-Morales, 1991; Cevallos-Ferriz, 1995) and as
float near Rancho la Fortuna (Text-fig. 34).

Fischer et al. (1995) presented columnar sections of

this member from Cerro Colorado, Cerro el Pleito, and
other western localities, where the unit is 50-52 m
thick; sections to the east at Agua Amarga, Tarabillas,
and Canada de la Luz are thinner, 39-44 m. The upper
boundary varies from a disconformity overlain by tuffs
and volcaniclastic rocks at Cerro Colorado and Cerro
el Pleito to a gradational contact in the San Juan de la
Costa area. There are no datable volcanic layers in the
Cerro Colorado Member, but Hausback (1984b) re-
ported an overlying rhyolite tuff of 21.0 + 0.4 Ma near
San Juan de la Costa.

Unnamed volcanic and volcaniclastic rocks, late
Early Miocene to early Late Miocene.—We preter to
call the rocks that unconformably overlie the El Cien
Formation unnamed volcaniclastic and volcanic rocks,

Nn
e)

except for the named tuffs of Hausback (1984a,b).
Many workers refer these rocks above the phosphatic
beds to the Comondu Formation of Heim (1922), but
lithologies and ages differ between the Magdalena em-
bayment and Sierra la Giganta areas. The type section
of the Comondu Formation is a distinctive volcani-
clastic boulder to cobble conglomerate unlike any fa-
cies in the Magdalena embayment. Ages vary from
12-14 Ma in the type area to 16-18 Ma for the San
Juan Tuff at Rancho Aguajito-San Juan de la Costa,
and 21—23 Ma for the La Paz rhyolite tuffs near San
Juan de la Costa (Hausback, 1984a,b).

Rancho el Aguajito de Castro
Plate 1, Column 19
(Text-fig. 33, Table 5, Appendices 1, 2)

Column modified from Carreno (1992b), Schwen-
nicke ef al. (1996), Schwennicke and Plata-Hernandez
(1997), and Fischer et al. (1995). Area is shown on
the El Conejo quadrangle, GI2D81, scale 1:50,000;
the locality maps of Fischer ef al. (1995); and the geo-
logic maps of Hausback (1984b) and Carreno (1992b).

Tepetate Formation, Early Eocene.—The Tepetate
Formation was discussed in the previous section and
in Table 5. R. W. Fulwider sampled the unit in 199]
at km 82 west of Rancho Aguajito de Castro and found
Early Eocene planktonic foraminifers; J. C. Ingle, Jr.
(written communication, 1991) identified benthic mi-
crofossils that suggest bathyal to shelf-edge depths.

Text-figure 30.—Magdalena Plain, map showing old ranchos and other landmarks. Map modified from J.T. Smith (1992) shows an old trail
used by early mappers: Nelson and the Biological Survey Expedition of 1905-1906; Heim in 1915; Beal in 1918; and Darton in 1920. Many
of their fossil localities bear the names of ranchos. Mina-Uhink (1957) reported Salada Formation in cores from Pozo Iray #2. The El Cien
Formation near El Mangle contains abundant mytilid molds. CSL, Cabo San Lazaro, PST, Punta San Telmo.

Text-figure 31.—Cerro Colorado (highest ridge) and Cerro Tierra Blanca (below and to the right), type sections of the El Cien Formation,
Cerro Tierra Blanca and Cerro Colorado Members. The lowest beds are the marine Cerro Tierra Blanca Member; the Cerro Colorado Member,
here a nonmarine facies, forms much of Cerro Colorado and is capped by unnamed Miocene volcaniclastic sediments. Photo, J. T. Smith,
1995.

Text-figure 32.—Arroyo San Hilario, type area of the San Hilario Member, El Cien Formation. View east at the ‘“Ten-minute locality” of
Applegate (1986) (= Instituto de Geologia Micropalentology locality 130 = Natural History Museum of Los Angeles County locality LACMIP
4830), approximately 3 km northeast of El Cien (km 100). The beds contain the Late Oligocene to Early Miocene index species Anadara
vanderhoofi Durham. Photo, T. M. Cronin, 1984.

Text-figure 33.—El Cien Formation, map showing type sections and study areas from Applegate (1986) and Fischer er al. (1995), Map
modified from Carreno (1992b); regional index map is shown in Text-figure 30, lithostratigraphic information in Table 5. A—D, study areas of
Fischer et al. (1995): A, El Cien Formation, all members of Applegate (1986); B, Arroyo Agua Amarga, part of composite type section of
San Juan Member and sections of Cerro Colorado Member: C, Canada de la Luz and Arroyo Tarabillas, outcrops of San Juan and Cerro
Colorado Members: D, Aguajito de Castro, part of composite type section of the San Juan Member. Reworked silicified wood (Text-fig. 34)
is found in the Cerro Colorado Member at Rancho la Matanza and near La Fortuna, Megafossil symbol in area A represents the **Ten-minute
locality” of Applegate (1986) in the San Hilario Member. Megafossil locality near Rancho la Fortuna is in a marine facies of the Cerro
Colorado Member. CC, Cerro Colorado and Cerro Tierra Blanca; CE, Cerro de la Estaca, Cerro Colorado Member, Instituto de Geologia
Micropalentology locality 1580; EC, El Cien, km 100; T, Rancho Tepetate.

Text-figure 34.—Silicified wood, float specimens from the El Cien Formation, Cerro Colorado Member, near La Fortuna. Photo, J. T. Smith,
1989.

54 BULLETIN 371

r
5 Rive

rad : ;
Salton color? a. Holocene b. Late Miocene ~ Early Pliocene

Trans-Mexican ,’, ¥
“volcanic belt *) ¥ =
marine water i Se
i t Soy, ¥"¥ volcanic belt vv y-
paleoshorelines Rio Balsas ? Py ‘’ volcar ic wy
- inferred shorelines Sierra La Victoria
mangroves La Trinidad

c. Middle Miocene - d. Early - early Middle e. Late Oligocene
early Late Miocene Miocene (30 - 23.7 Ma)
(15 - 8 Ma) (23.7 - 15 Ma)

Sierra
La Trinidad

Text-figure 35.—Paleogeography of the Baja California Peninsula and ancient Gulf of California, map based on distributions of Late
Oligocene to Holocene marine mollusks and associated microfossil and radiometric data. Map after J. T. Smith (199 1c: fig. 5), OAAPG 1991,
reprinted by permission of the American Association of Petroleum Geologists, whose permission is required for further use. Present outline
of Baja California and the eastern gulf shoreline shown in part, for reference. 35c¢ includes the protogulf of Fenby and Gastil (1991), whose
subsurface marine sediments extend an unknown distance to the east. A, Acapulco; E, Ensenada; EC, El Cien: G, Guaymas; IT, Isla Tiburon;
LM, La Mision; LP, La Purfsima; PM, Punta Mita; PP, Puerto Penasco; PST, Punta San Telmo; PV, Puerto Vallarta; R, Rancho El Refugio;
SD, San Diego: SF San Felipe: SGP. San Gorgonio Pass: SI, San Ignacio; SJC, San Juan de la Costa; SR, Santa Rosalia; TS, Todos Santos;
3M, Islas Tres Martas

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

San Juan Member, Late Oligocene.—Only the mid-
dle and upper parts of San Juan Member of the El Cien
Formation crop out in the El Cien-Aguayito area,
where the 75-m-thick section is unconformable on bio-
turbated silt and sandstones of the Tepetate Formation.
Fischer er al. (1995) described a prominent 0.2- to 4-
meter-thick fossiliferous basal conglomerate in Arroyo
Aguayjito that is overlain by 20 m of siltstone and sand-
stone. The unit is conformably overlain by the Cerro
Colorado Member.

The San Juan Member is exposed along parallel out-
crop belts of a syncline that trends north-northwest to
south-southeast. One limb lies northwest of San Juan
de la Costa, the other extends from north of Cerro
Colorado to Rancho el Aguajito de Castro near km 68
on Mexico 1. Lithologies vary between western and

eastern areas, as shown in detailed sedimentological
studies by Schwennicke (1992, 1994). The Late Oli-
gocene age is based mainly on dated tuffs, diatom, and
planktonic foraminiferal zones at Arroyo San Hilario;
calcareous nannofossils from the middle part of the
San Juan Member at Arroyo Aguayito represent nan-
nofossil zones NP 24/NP 25 (Schwennicke, 1992).

Cerro Colorado Member, Early to Middle Mio-
cene.—Detailed studies by Schwennicke (1992, 1994)
and Gidde (1991) at a number of localities identified
the regressive nature of the Cerro Colorado Member

from shallow marine to nonmarine conditions. At Ran-
cho el Aguayito de Castro the member is Early Mio-
cene or older, constrained by the La Paz tuff, 24 Ma,
in the overlying volcaniclastic sediments (Hausback,
1984a,b).

Todos Santos, Arroyo la Muela,
southern Baja California Sur

Overview

Southwest of La Paz and approximately 10 km
north of the town of Todos Santos, highway Mexico
19 crosses a wide arroyo that drains the western side
of the Sierra la Laguna and exposes Miocene marine
deposits along its northwestern wall. The large stream
bed has many names, including Arroyo la Muela on
the published El Rosario quadrangle, Arroyo San Juan
of Beal (1948), Arroyo Playita of Mina-Uhink (1957),
and Arroyo Grande of J.T. Smith (1992). The highway
has changed many times due to flooding: access to
fossil oucrops in Arroyo la Muela became more dif-
ficult after the summer of 1972.

Aranda-Gomez and Pérez-Venzor (1989) studied the
igneous and metamorphic rocks of the La Paz Crys-
talline Complex near Todos Santos and included ap-
proximately 10 km? of Salada Formation outcrops on
their map (1989: text-fig. 3). The southwestern part of

nn
nN

the Baja California peninsula is underlain by prebath-
olithic metamorphic basement rocks and the Creta-
ceous granitoid plutons that intruded them, but the Ce-
nozoic rocks have not been studied in detail. They lie
to the west of the La Paz Fault and the Los Cabos
Block. Beal (1948) named the La Paz Fault and
mapped three separate areas west of the road between
Arroyo Grande and Todos Santos as “*Ts,”” Salada For-
mation. Reconnaissance field work by J. T. Smith, S.
Pedrin-Avilés, G. Padilla-Arredondo, and E. Diaz-Ri-
vera encountered only Quaternary gravels in the south-
ern two areas.

Arroyo la Muela
Plate 1, Column 20
(Text-figs. 36, 37, 73 Appendices 1, 2)

Column modified from Aranda-Gomez and Pérez-
Venzor (1989) and Schwennicke ef al. (2000). The
area is Shown on El Rosario Quadrangle, F12B23, 1:
50,000; and the geologic maps of Beal (1948, and un-
published field sheets in Stanford University’s Branner
Earth Sciences Library and Map Collections), Mina-
Uhink (1957), and Aranda-Gomez and Pérez-Venzor
(1989: figs. 3, 21).

Marine fossils were discovered in Arroyo la Muela
by James C. Ingle, Jr, and students during a spring
break in 1972. The unit was sampled by J. T. Smith,
T. E. Fumal, and J. J. Aranda-Gomez in 1983 and by
J. T. Smith and T. M. Cronin in 1984. Schwennicke
(written communication, 1999) reported additional
outcrops to the north, and Martinez-Gutiérrez and Jo-
rajurta-Lara (2002) found land vertebrates of probable
Late Miocene age at La Matanza near Rancho Carrizal
during a survey of the El] Carrizal Fault.

Stratigraphy

La Paz Crystalline Complex, Cretaceous.—Prebath-
olithic basement and crystalline rocks of the south-
western Cape region belong to the La Paz Crystalline
Complex (El Complejo Cristalino de La Paz) named
by Ortega-Gutiérrez (1982) and discussed by Aranda-
Gomez and Pérez-Venzor (1989). These authors de-
scribed several informal units of metamorphosed Me-
sozoic rocks east and north of Todos Santos and Punta
Lobos. Oldest to youngest they include the Punta Lo-
bos gneiss, Todos Santos marble, and El Cardonozo
phyllite. The La Buena Mujer tonalite, which has an
K/Ar age of 98 Ma, intruded the older metamorphic
rocks (Aranda-Gomez and Pérez-Venzor, 1989).

Salada Formation, late Middle Miocene to Late
Miocene.—Described by Heim (1922) from a section
170 km to the north, the Salada Formation is repre-
sented along the northwestern side of Arroyo la Muela

56 BULLETIN 371

Text-figure 36

Arroyo la Muela, north of Todos Santos, B.C.S.,
where the weathered Salada Formation forms pink, green, and brown
badlands topography. Arrow indicates level of the bench where ma-

rine fossils are found (Text-fig. 37). Photo, T. M. Cronin, 1984

by loosely consolidated marine and nonmarine arkosic
sediments. Several facies of the unit, whose base is
not exposed, extend perhaps 1.5 km along the arroyo
at the base of a ridge known as la loma El Bayo Flojo
(Text-fig. 36). A northwest-trending normal fault of the
Vinaterta-La Matanza Fault System forms the north-
eastern contact between the Salada Formation and Ho-
locene gravels (Aranda-Gomez and Pérez-Venzor,
1989: figs. 3, 21).

Schwennicke (written communication, 1999) esti-
mated a thickness of 36 m for the sequence of green-
ish, pink, and brown mottled siltstone, well-indurated
limy sandstone and conglomerate, and _ fine-grained,
loosely consolidated, granitic sandstone with angular
pebbles and weathered phenocrysts. The rocks dip 5
west-southwest and weather to pink and green bad-
lands topography. Megatossils are mainly internal
molds of bivalves and gastropod shells replaced by
calcite; they commonly weather out on the surface of
a meter-high bench (Text-fig. 37). Shallow-water gas-
tropods include Architectonica nobilis R6ding, Turri-
tella abrupta fredeai Hodson, Cancellaria (Pyruclia)
diadela Woodring, Cymia sp. ct. C. michoacanensis
Perrilliat, Phos sp. ct. P. crassus Hinds, and Vasum
haitense (Sowerby): vertebrates are represented by
shark teeth, myliobatid ray plates, whale teeth, and a
camelid humerus (J. T. Smith, 1992).

Age and correlation of the Salada Formation in Ar-
royo la Muela.—The beds were regarded as Pliocene
by Beal (1948) and Plio—Pleistocene by Aranda-Go-
mez and Pérez-Venzor (1989), but reconnaissance pa-

Text-figure 37

Salada Formation, coquina and sandstone facies
in one-meter-high bench at the base of la Loma el Bayo Flojo. Photo,
[. M. Cronin, 1984

leontological collections indicate a Miocene age for
the lower marine facies (J. T. Smith, 1992). Ongoing
studies by Schwennicke ef al. (2000) identified Middle
Miocene shark teeth in Arroyo la Muela, and they sug-
gested that the unit there could be older than the type
section at Arroyo la Salada.

It is not Known how these outcrops relate to oyster-
bearing marine rocks 20 km to the north or to unnamed
lower Miocene whale-bearing sediments 50 km to the
north near Rancho la Palma, northwest of San Pedro
(Text-fig. 73, p. 95). The vertebrates that Schwennicke
et al. (1996) excavated from dark green laminated,
tuffaceous mudstone above a basal conglomerate rep-
resent a cetotheriid baleen whale of an early evolu-
tionary stage.

Many of the mollusks in the Salada Formation in
Arroyo la Muela are Tertiary-Caribbean species that
correlate the section with the upper part of the Trinidad
Formation, Subunit A of McCloy (1984) in the San
José del Cabo Trough and with Miocene marine units
in Panama, Colombia, Trinidad (formerly B.W.1.), and
the Dominican Republic. Some of the same species
were also reported from the Ferrotepec Formation of
the La Mira Basin of Michoacan, mainland west Mex-
ico (Perrilliat, 1981, 1987; J. T. Smith, 1992).

Gravels of Cerro la Bandera, informal name, Pleis-
tocene to Holocene.—Coarse sediments are informally
referred to the gravels of Cerro la Bandera (la grava
del Cerro Bandera) by Aranda-Gomez and Pérez-Ven-
zor (1989). The unit is discordant on the Salada For-
mation west of Mexico 19 and on the crystalline com-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

plex east of the highway, from which the flat-lying
gravels and unconsolidated arkosic sands were eroded.
They are named for a small hill in Arroyo Grande
northwest of Microondas San Pedro (km 41 on Mexico
19). Quaternary alluvium and beach deposits overlie
the gravels.

PART II: ANCIENT AND MODERN
GULF OF CALIFORNIA

SALTON TROUGH, CALIFORNIA, TO
ISLAS TRES MARIAS,
SOUTHERN GULF OF CALIFORNIA

Salton Trough
Plate 2, Columns 21, 22, 23, 24
(Text-figs. 1, 2, 38, Appendices |, 2)
Geographic Overview

The Salton Trough covers an area approximately
200 km long by 150 km wide. It extends from south
of the San Bernardino Mountains in the San Gorgonio
Pass and Whitewater River area, California, to the
Gulf of California, Mexico. It lies east of the Penin-
sular Ranges and the Elsinore Fault, west of the Oro-
copia and Chocolate Mountains and other desert rang-
es. The western Salton Trough includes the Imperial
Valley and the Fish Creek and Vallecito Mountains;
the eastern part includes the Bouse embayment (Text-
fig. 38). Stratigraphy is complicated by many facies
that change rapidly; they are folded, faulted, over-
turned, and they wedge out in some places. At the
deepest part of the trough, Neogene (primarily Plio—
Pleistocene) sediments are estimated to exceed 6 km
(20,000 ft) in thickness (Dibblee, 1996). Woodring
(1931, 1932), Allen (1957), and Winker (1987) sum-
marized earlier papers on the stratigraphy of the area
and showed formation assignments according to nu-
merous workers.

The area has a complex geologic history that in-
cludes multiple seawater incursions from the south, the
Early Pliocene arrival of Colorado River deltaic sedi-
ments from the east, and Late Miocene to present
structural offsets along the major fault zones, which
include the Elsinore, San Jacinto, and San Andreas
Fault Systems. There are two onshore spreading cen-
ters, one at Brawley, south of the Salton Sea, the other
south of Mexicali between the Imperial and Cerro
Prieto Faults (Mueller and Rockwell, 1991). The struc-
tural setting of the area is discussed in papers edited
by Powell et al. (1993).

The Salton Trough ts the northernmost extension of

the ancient Gulf of California; geologists recognize
that the northern sections mapped as the Imperial For-
mation were deposited as much as 180 km to the
southeast and displaced to their present locations by

n
~

Late Miocene to Early Pliocene faulting (Matti and
Morton, 1993). These authors included detailed maps
showing the relation of key outcrops to the main and
subsidiary strands of the San Andreas Fault. Other pa-
pers, including those by McDougall er al. (1999) and
Dibblee (1996a,b), updated the extensive literature on
the stratigraphy of the area.

Multiple Cenozoic marine incursions in the
Salton Trough

Paleontological and radiometric data suggest that
there have been as many as three Neogene seawater
incursions in the northern gulf (McDougall, 1996; Mc-
Dougall et al., 1999), which explains the long-standing
disagreements between authors arguing for a Miocene
versus a Pliocene age of the Imperial Formation.

First incursion of the ancient gulf, late Middle Mio-
cene.—The presence of a late Middle to Late Miocene
gulf is inferred from rare Middle Miocene marine mi-
crofossils in isolated occurrences from the northern
Salton Trough to wells in the Yuma area and coastal
Sonora. Gastil ef al. (1999) interpreted an unnamed
megatfossiliferous marine conglomerate at Isla Tibu-
ron, Sonora, as evidence of this incursion. The section
contains a 12.9 Ma volcanic breccia and abundant fos-
sil mollusks, including species of Atrina, Lyropecten,
Spondylus, Cardita, and Pycnodonta (Crenostrea),
which are also present in the northernmost Salton
Trough in reworked sediments east of the Whitewater
River. The unit at Isla Tiburon is overlain with angular
unconformity by an ash-flow tuff of 11.2 Ma and cut
by younger dikes of 4.16 + 1.8 Ma and 5.67 + 0.17
Ma.

McDougall er al. (1999) noted the presence of re-
worked rare Middle Miocene nannofossils in the
Whitewater section in the lower Imperial Formation
“worm tube” bed between unnamed lower and upper
parts of the unit. The calcareous nannoplankton spe-
cies Cyclicargolithus floridanus (Roth and Hay) be-
came extinct in Middle Miocene Zone CN5a, Sphen-
olithus heteromorphus Deflandre in Zone CN4 (a com-
bined range of 16-13 Ma); their presence in the
“worm tube” bed indicates that *
older than Late Miocene were once present in this
area” (McDougall et al., 1999). These authors also
reported Middle Miocene taxa from higher in the sec-
tion, where ~*

. marine deposits

. they are rare and more poorly pre-
served than the associated [Late Miocene—Early Plio-
cene] microflora, and they occur in samples interpreted
as having a significant greater amount of transported
sediment.” Those sediments were referred to the un-
named upper member of the Imperial Formation and
to shale lenses and reworked channel deposits in the

(10)

Riverside.

San Gorgonio Pass

Edge of Salton Trough
Gypsum quarry

Active spreading center
(pull-apart basin)

Key Neogene marine
& nonmarine deposits

BULLETIN 371

CALIFORNIA

—

Little San
Bernardino

“Sx. Mountains

faces “+ Bouse

| Parker

ie are 34°N
Bouse embayment

(saline lake deposits)

EID)
Orocopia
Mountains

Cibola ).

Cargo Muchac
Mountains

" pede Prieto
Ly me

CALIFORNIA

Blyite-[- 2: ) 2
ee

{ARIZONA

. ZTrigo _
_ Mountains

33°N

San Luis & |
\Fortuna Basins

Wagner
Basin

Puertecitos

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH S59

unconformable overlying Painted Hill Formation (Mc-
Dougall er al., 1999; Murphy, 1986). They are strati-
graphically below a basalt flow in the Painted Hill For-
mation that has K/Ar ages of 6.04 + 0.18 Ma and 5.94
+ 0.18 Ma (J. L. Morton in Matti et al., 1985).

Hydrothermally altered, poorly preserved, Middle
Miocene foraminifers identified as Cassigerinella chi-
polensis (Cushman and Ponton) were listed from two
wells in the Cerro Prieto geothermal field (Cotton and
Vonder Haar, 1979). P. B. Smith in Lucchita (1972)
noted “*... a puzzling abundance of Bolivina guadal-
upae Parker characteristic of the Middle and Late Mio-
cene of California” from the Yuma, Arizona area. Ma-
rine Miocene rocks were reported from wells in the
basin south of Yuma, Arizona (Mattick ef al., 1973),
and in the subsurface of coastal Sonora (Lozano-Ro-
men, 1975; Gomez-Ponce, 1971; King, 1939).

Second incursion of the ancient gulf, late Miocene
to earliest Pliocene.—A Late Miocene incursion be-
tween 9 Ma and 6 Ma is represented in the San Gor-
gonio Pass area of the northern Salton Trough by the
upper member of the Imperial Formation, which is in-
terpreted as 6.0—7.4 Ma in the Cabazon and White-
water River sections (McDougall ef al., 1999). These
authors reported a Late Miocene to earliest Pliocene
faunule that includes the benthic foraminifers Amphis-
tegina gibbosa ad Orbigny, Cassidulina delicata Cush-
man, and Uvigerina peregrina Cushman, planktonic
foraminifers from zones N1I7—N19, and = calcareous
nannoplankton from Calcareous Nannoplankton Zones
CN9-NNI1. Dean (1988, 1996) listed four of the
same Late Miocene calcareous nannoplankton index
species from claystones intercalated with the Fish
Creek Gypsum in the Fish Creek Mountains: Braa-
rudosphaera bigelowti (Gran and Braarud) Deflandre,
Coccolithus pelagicus (Wallich) Schiller, Reticulofe-
nestra pseudoumbilica (Gartner), and Sphenolithus
abies Deflandre. Quinn and Cronin (1984) and Ingle
(1974) reported similar Late Miocene Planktonic Fo-
raminiferal Zone N17 microfossils, including Amphis-

tegina gibbosa ad’ Orbigny, from the lower part of the
Imperial Formation in Fish Creek Wash in the Valle-
cito Mountains.

Miocene to Pliocene marine microfossils were also
collected from a section in the Sierra Cucupa east of
Laguna Salada (Vazquez-Hernandez et al., 1996; Mar-
tin-Barayas ef al., 2001).

As discussed by Ingle in Gastil et al. (1999), inner
to outer neritic foraminiferal assemblages from south-
western Isla Tiburon indicate an age of latest Miocene
to Early Pliocene Planktonic Foraminiferal Zones
N1I7B-—-N19 for the white sandstone facies mapped as
Unit M8c. The planktonic and benthonic foraminifers
include a number of taxa that range from Miocene to
Holocene, some currently living in the Gulf of Cali-
fornia. Species lists for the upper part of the Imperial
Formation in the San Gorgonio Pass area and Unit
M8c of southwestern Isla Tiburon have some taxa, in-
cluding Amphistegina gibbosa d@ Orbigny, in common
(McDougall et al., 1999; Ingle in Gastil er al., 1999).
Gastil et al. (1999) acknowledged but could not ex-
plain the discrepancy between dates based on latest
Miocene-earliest Pliocene microfossils from Unit M8c
that correspond to 6.4—4 Ma and the late Middle to
early Late Miocene age based on megafossils from
Unit M&d associated with radiometric dates of 12.9 Ma
and 11.2 Ma from underlying and overlying volcanic
rocks.

Third incursion of the ancient gulf, Early Plio-
cene.—The youngest incursion, at 5—3 Ma, is repre-
sented by foraminifers of Early Pliocene Planktonic
Foraminiferal Zone N19/20 in sediments surrounding
the Fish Creek and Vallecito Mountains that precede
and post date the Early Pliocene arrival of Colorado
River deltaic sediments in the Fish Creek and Valle-
citos area no later than 4.3 Ma” (Winker and
Kidwell, 1986, 1996), based on magnetostratigraphic
ages from Johnson er al. (1983). Sediments record the
marine—nonmarine transition at 4.0 Ma and the pres-
ence of the Colorado River in the western Salton

Text-figure 38.

Salton Trough, map of the ancient Gulf of California, northern part from San Gorgonio Pass to San Felipe, B.C. Map

compiled from McDougall et al. (1999), Vazquez-Hernandez er al. (1996), Mueller and Rockwell (1991), Kidwell (1988), Winker and Kidwell
(1986), and Dillon ez al. (1993). Active spreading centers, north to south, are Brawley, Cerro Prieto, Wagner Basin. Abbreviated fault names:
MCE. Mission Creek and BE Banning strands of the San Andreas San Fault; CR, Canon Rojo Fault; [IR Imperial Fault; LSE Laguna Salada
Fault; PME, Pinto Mountain Fault: SME Superstition Mountain Fault. Place names: AC, Alverson (Fossil) Canyon; B, Brawley: FCM, Fish
Creek Mountains, including Split Mountain Gorge, Fish Creek Gypsum quarry, and Barrett Canyon, which flows south to Carrizo Creek. GH,
Garnet Hill; PS, Palm Springs; SS/BB, Superstition Hills and Borrego Badlands; VM, Vallecito Mountains. The northern side of the Coyote
Mountains includes Vallecito Badlands, Carrizo Badlands, and Garnet Canyon; the southern and southeastern sides include Alverson Canyon,
the Flat Iron, and Painted Gorge. Earlier workers interpreted the Bouse embayment as an extension of the northern gulf, but based on field-
work, Ehlig in Dillon and Ehlig (1993) and Spencer and Patchett (1997) regarded the travertine and fossiliferous sediments north of Cibola,
Arizona, as saline lake deposits, not marine in origin. The San Luis and Fortuna Basins south of Yuma contain subsurface Neogene marine
sediments (McDougall er al., 1999).

60 BULLETIN 371

Trough until 2.8 Ma (date interpolated by Johnson er
al., 1983).

The eastern Salton Trough, which includes the area
called the Bouse embayment, is underlain by the Late
Miocene to Pliocene Bouse Formation, a unit that is
correlative with parts of the Imperial Formation. A
tuffaceous horizon at the base of the Bouse Formation

is 5.47 + 0.20 Ma, slightly older than the arrival of

the first Colorado River sediments in the eastern Salton
Trough (P. B. Smith, 1970; Damon er al., 1978; Shat-
iquallah er al., 1980). Buising (1990) reported widely
varying radiometric ages for a tuffaceous horizon from
Milpitas Wash, 30 km south of Cibola, Arizona: 8.1]
+ 0.5 Ma (Metzger et al., 1973), 5.47 + 0.20 and 3.02
* 1.15 Ma (Damon in Metzger et al., 1973). She re-
garded the Bouse Formation as marine to brackish wa-
ter: Spencer and Patchett (1997) interpreted it as la-
custrine.

Correlating the Imperial Formation,
a time-transgressive unit

Before marine units from south of the border can be
related to the northern outcrops of the ancient gulf, it
is important to know ages and lithologies of particular
sections. Rocks mapped as the Imperial Formation
range from approximately 9-3 Ma, latest Middle or
Late Miocene to Middle Pliocene. Multiple seawater
incursions, rapid facies changes, reworked sediments,
and deformation within active fault zones and devel-
oping basins contribute to complex stratigraphic rela-
tionships that are best understood from a multidisci-
plinary perspective. In one such study, Kidwell (1988)
used sedimentation and the taphonomy of shell beds
and skeletal concentrations within the Imperial For-
mation to assess the fossil record of a recently rifted
continental margin.

Paleontology at the species level can measure pack-
ages of time, rates of change, depositional environ-
ment, and provincial affinities. With more information
about key sections of the Imperial Formation, the lo-
cation and age of its oldest sediments and significant
marker beds, and improved resolution based on fossil
species, a unit that transgressed as much as six million
years can be used to relate the ancient Gulf of Cali-
fornia to a more specific tectonostratigraphic context.
Marine deposits containing isolated, reworked micro-
fossils can be better understood, and meaningless cor-
relations in the literature with “the Imperial’? can be
avoided once outcrop areas and stratigraphic intervals
are specified. Maps showing specific localities are be-
yond the scope of this paper; cited references and to-
pographic maps should be consulted for details.

Representative columns of the Salton Trough

We include four columns, from north to south: east
of the Whitewater River, Riverside County, California:
the Fish Creek and Vallecitos Basin, Riverside County,
110 km to the south; the southern Coyote Mountains,
Imperial County, California, 25 km further south; the
Sierra Cucupa, Cerro Prieto and Laguna Salada area,
Baja California, 50 km further southeast.

Basement rocks in all the columns are late Creta-
ceous plutonic rocks of the Peninsular Ranges batho-
lith or the Paleozoic metasedimentary rocks they in-
truded (see summary by Dibblee, 1996a). At times the
metamorphic rocks of the Coyote Mountains and ton-
alites in the Fish Creek and Vallecito Mountains stood
as islands in the ancient gulf and provided substrata
for shallow water attached and boring organisms.

Table 6 summarizes lithostratigraphic units in the
ancient Gulf of California from the San Gorgonio Pass
to the Sierra Cucupa.

Whitewater River—San Gorgonio Pass area
Plate 2, Column 21
(Text-figs. 1, 2, 38, 39, Table 6, Appendices 1, 2)

Column modified from Allen (1957) and McDou-
gall er al. (1999); area is shown on the Whitewater,
Desert Hot Springs, and Cabazon 72-minute and Palm
Springs 15-minute quadrangles, California. Outcrops
are shown on the maps of Allen (1957) and Matti er
al. (1985).

Overview

Our column includes the northernmost outcrops of
the Imperial Formation in the Salton Trough. The unit
is exposed in an unnamed south-flowing tributary to
Super Creek over a relatively small area in the NW %
Section 1, T 3S, R 3 E and SW 4% Section 36, T 2 S,
R 3 E, Whitewater River 74-minute quadrangle. The
section is southwest of Painted Hill, in an area used
for many years to orient students from the University
of California, Riverside, to field geology (Murphy,
1986). Bramkamp (1935a,b), Allen (1957), and Mc-
Dougall er al. (1999) discussed contemporaneous out-
crops near Cabazon, 12 km to the west.

Stratigraphy

Coachella. Fanglomerate, Late Miocene.—In the
Whitewater area, the Coachella Fanglomerate forms
cliffs along the eastern side of the Whitewater River,
approximately 6.4 km north-northwest of Painted Hill,
the prominent orange-colored peak seen from the un-
named canyon where the Imperial Formation is ex-
posed. The locally-derived sediments contain Late
Miocene olivine basalt flows and volcanic breccias that

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 6l

constrain the age of the unconformable overlying Im-
perial Formation to younger than 10.1 + 1.2 Ma (D.
Krummenacher i Peterson, 1975). Peterson (1975) in-
terpreted the unit as an alluvial fan that originated to
the north and was deposited in a deep basin.

Imperial Formation, Late Miocene—Early Plio-
cene.—The Imperial Formation was named for a sec-
tion in the southern Coyote Mountains; it has been

applied to marine deposits from many sediment sourc-
es in widely separated areas. East of the Whitewater
River the unit is limited to discontinuous narrow out-
crops over a distance of 1.6 km between two strands
of the San Andreas Fault (Text-fig. 39). It consists of
30 m of locally-derived, steeply dipping to overturned
sediments that pinch out upcanyon and rest noncon-
fomably on crystalline basement at the lower end of
the arroyo (Allen, 1957; McDougall et a/., 1999). Far-
ther north the beds are unconformable on the Coach-
ella Fanglomerate, whose interbedded basalt flow con-
strains the Imperial Formation in this area to younger
than early Late Miocene.

The lower part of the section includes channel de-
posits in the underlying rocks, coarse- to medium-
grained sandstone, and conglomerate. Mollusks, in-
cluding articulated pectinids, Spondylus, and oysters,
are found in the basal breccias (Murphy, 1986).

A distinctive yellowish-gray, one-meter-thick
“worm tube bed” of siltstone and sandstone separates
the two members of the Imperial Formation. It con-
tains detached, fragmented, and randomly oriented cal-
careous tubes (Whether they include only worms or
also vermetid gastropods has not been determined) and
microfossils that indicate transported sediments depos-
ited at outer neritic depths up to 152 m (McDougall
et al., 1999). The upper member is a medium- to fine-
grained sandstone and siltstone that interfingers and
can also be in unconformable contact with the Painted
Hill Formation, although the boundary is commonly
obscured by alluvium. McDougall er al. (1999) de-
tailed the micropaleontology of this section and cor-
relative beds near Cabazon, which they interpreted as
deeper water, “possibly upper bathyal (152—244 m).”
Upsection from the “worm tube bed” they also noted
shallowing and warming trends that correspond to
global sea-level and paleotemperature trends at 6.5—
6.3 Ma.

Murphy (1986) and his students studied the ““worm
tube bed” and a yellowish-gray micaceous silt facies
before the unit was over-collected; they observed **. . .
abundant specimens of Atrina in living position
with the most diverse fauna in the formation.”” Bram-
kamp (1935b) and Powell (1986, 1988) illustrated
some of the articulated marine mollusks, barnacles,

and corals that are no longer easy to find. These mol-
lusks and those that are reworked in the channel brec-
clas, many with Caribbean affinities, are also known
from the late Middle or early Late Miocene marine
conglomerate on Isla Tiburon (J. T. Smith, 1991c, and
in Gastil et al., 1999),

Bryozoans, brachyuran crabs, corals, and baleen
whales have also been reported from the Whitewater
area (Text-fig. 39 and Appendix 1). The megafossil
collections can be seen at the University of California,
Riverside, the University of California, Berkeley Mu-
seum of Paleontology, and the Natural History Mu-
seum of Los Angeles County.

Age and correlation of the Imperial Formation,
northernmost Salton Trough, Late Miocene—Early Pli-
ocene, with reworked Middle Miocene fossils.—Age-
diagnostic foraminifers and nannoplankton indicate a
Late Miocene to Early Pliocene age of 7.4 Ma to older
than 6.04 Ma for the Imperial Formation in the White-
water and Cabazon (also known as Lion Canyon) sec-
tions; McDougall er a/. (1999) favored an age of 7.4—
6.0 Ma based on sea-level fluctuations, paleotemper-
ature, and radiometric data from adjacent units. They
referred the microfossils to Planktic Foraminiferal
Zones NI7—-N19 and Calcareous Nannoplankton
Zones CN9-CNI1 of Okada and Bukry (1980). Spe-
cies lists include such Late Miocene—Early Pliocene
index species as the benthic foraminifers Cassidulina
delicata Cushman, Uvigerina peregrina Cushman, and
Amphistegina gibbosa dOrbigny; planktic foramini-
fers Globogerinoides obliquus Boll, G. extremus Bolli
and Bermudez, and Globigerina nepenthes Todd; cal-
careous nannoplankton Sphenolithus abies Deflandre
and Reticulofenestra pseudoumbilicata (Gartner).
They also listed Discoaster brouwert Tan Sin Hok
emend. Bamlette and Riedel, D. sp. aff. D. surculus
Martini and Bramlette, and Sphenolithus neoabies De-
flandre of Calcareous Nannoplankton Zones CN9a—
CN11. The assemblage corresponds to the microfossils
reported by Dean (1996) from siltstone layers in the
Fish Creek Gypsum.

McDougall er al. (1999) also found rare, poorly pre-
served Middle Miocene microfossils in the “worm
tube bed” and in channels and siltstone deposits of the
lower Painted Hill Formation. They identified the cal-
careous nannoftossils Cyclicargolithus floridanus (Roth
and Hay) and Sphenolithus heteromorphus Deflandre,
which became extinct in zones CN5a and CN4 (16—
13 Ma), respectively. Reworked taxa were sparse and
less well preserved than younger microfossils; the
samples with a mixed fauna had a greater amount of
transported sediment.

Other northern outcrops of the Imperial Formation

BULLETIN 371

Table 6.—Salton Trough, California and Baja California, lithostratigraphic units (Text-fig. 38). Lowercase names indicate informal units that
were not established according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Alverson Formation

Anza Formation

Canebrake Conglomer-
ate

Canon Rojo conglom-
erate, informal name

Coachella Fanglomer-
ate

Colonia Progreso vol-
canics, informal
name

Fish Creek Gypsum

Imperial Formation

Tarbet in Tarbet and Holman

(1944) and Tarbet (1951).
Woodward (1974) called Al-
verson Andesite volcanic fa-
cies of the Anza Formation.
Winker and Kidwell (1996) re-
named the Elephant Trees for-
mation, informal name, of the
Split Mountain Group.

Woodward (1974) renamed the

sediments below the Alverson
Andesite. Kerr (1984) referred
Fish Creek Mountains out-
crops to the Red Rock forma-
tion, informal name.

Dibblee (1954).

Vazquez-Hernandez er al.

(1996).

E. Vaughan (1922). Allen
(1957) and Peterson (1975)
elaborated on the description.

Barnard (1968).

Dibblee (1954). Dean (1996) re-

ported interbedded marine

claystone layers.

D. Hanna (1926) renamed the
basal part of the preoccupied
Carrizo Formation of Kew
(1914). Later workers subdi-
vided the formation into the:
“Latrania sands,” “Coyote
Mountain Clays,” and ‘*Yuha
reefs.” uppermost clays with
oyster biostromes. Woodring
(1931, 1932) amplified the
lithologic descriptions. Dibblee
(1996a.b) refined the strati-
graphic nomenclature and sug-
gested a more representative
type section.

Formation was originally proposed for a sequence of nonmarine sand-
stones and volcanic flows. Type section is in Fossil Canyon (for-
merly Alverson Canyon), in the southern Coyote Mountains, Carri-
zo Mountain 72-minute quadrangle. Dibblee (1996a,b) referred to
the volcanic part as the Alverson Volcanics, 130 m (400 ft) of
dark-colored vesicular olivine basalt and minor basaltic andesite
and tuff-breccia. Early to early Middle Miocene, based on a 16 +
1.0 Ma basalt (Eberly and Stanley, 1978) and other radiometric
dates ranging from 22 to 14 Ma (Kerr and Abbott, 1996).

Unit is a reddish brown, coarse-grained sandstone and arkosic conglomer-
ate described from the eastern Fish Creek Mountains, southern part of
the Borrego Mountain SE 72-minute quadrangle [sections 25 and 36,
T 13S, R 8 E]. Kerr (1984) described a section 8 km southeast of
Split Mountain Gorge in Red Rock Canyon, Carrizo Mountain NE
72-minute quadrangle. Early Miocene.

Unit is a coarse conglomerate and sandstone with a maximum thick-
ness of 2,100 m (7,000 ft); it is a western marginal facies of parts
of the Palm Spring and Imperial Formations (Dibblee, 1996).
Named for Canebrake Wash, but type section is to the north in the
Vallecitos Badlands, Agua Caliente Springs and Arroyo Tapiado
7¥2-minute quadrangles. Plio—Pleistocene.

Unit consists of locally-derived fanglomerate that was described from
the southwestern Sierra Cucupa and northern Sierra Mayor where
the Laguna Salada and Canon Rojo faults form a pull-apart basin,
Sierra Cucupa quadrangle (Mueller and Rockwell, 1991). Dorsey
and Martin-Barajas (1999) referred the unit to the Canon Rojo red-
bed sequence. Plio—Pleistocene.

Unit consists of 1,500 m of east-dipping nonmarine, well-indurated, sand-
stone, gray-green Claystone, siltstone, and fanglomerate with minor ba-
salt. Sediments are deeper orange upsection as volcanic components
increased, Type section is at the Whitewater Trout Farm, eastern side
of Whitewater Canyon and 6.4 km (4 mi) upstream from Bonnie Bell,
Whitewater 7!2-minute quadrangle. Originally regarded as Quaternary
(FE. Vaughan, 1922), it contains a series of olivine basalt flows and
volcanic breccias 250 m above the base; one flow has a K-Ar age of
10.1 * 1.2 Ma (D. Krummenacher i Peterson, 1975).

Andesitic and dacitic volcanic breccias overlie granodiorite basement
in the northeastern Sierra Cucupa near the Colonia Progreso section
of western Mexicali, in the quadrangle of the same name. Middle
Miocene, based on a K-Ar age of 15.3 + 0.8 Ma (Barnard, 1968).

Unit consists of a 30 m (100 ft) thick section of white and tan-col-
ored gypsum and anhydrite with intercalated marine claystones in
the northwestern Fish Creek Mountains. Type area 1s northeast of
Split Mountain Gorge in a U.S. Gypsum Co. quarry, Borrego
Mountain SE 72-minute quadrangle. Late Miocene, based on cal-
careous nannoplankton in the claystone partings (Dean, 1988: K.
McDougall, oral communication, 1998).

Formation includes beds of coral fragments, shallow marine and del-
taic sandstones and siltstones, and claystones with oyster shells.
Hanna (1926) used Imperial Formation for only the basal 200 m
(650 ft) reworked beds. Neither he nor Woodring specified a type
section, although it was always regarded as Fossil Canyon in the
southern Coyote (formerly Carrizo) Mountains. Dibblee (1996a,b)
designated a 1,000 m (3,300 ft) thick type section in the Vallecito
Badlands between the Fish Creek and Coyote Mountains, near the
area where Kew (1914) mapped the “‘Carrizo Formation” (Arroyo
Tapiado and Carrizo Mountain NE 72-minute quadrangles). The
formation is Late Miocene and Early Pliocene, deposited during
successive seawater incursions; ages are based mainly on microfos-
sils, dated rocks in adjacent units, and stratigraphic position. Late
Miocene in the northern Salton Trough; Late Miocene—Early Phio-
cene in the Fish Creek Mountains and Vallecito Badlands (McDou-
gall et al., 1999). Miocene/Pliocene boundary, 5 Ma, and older in
the Coyote Mountains, based on a dated pectinid from the Painted
Gorge 72-minute quadrangle (J. T. Smith i Gastil er al., 1999).
Rare reworked Middle Miocene fossils in some sections.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 63

Table 6.—Continued.

Lithostratigraphic unit Author, reference

Lithologic description, type locality, age

Latrania Sand Member G. D. Hanna (1926); Woodring
(1931, 1932) elaborated on the
description; Keen and Bentson
(1944) first listed as a member
of the Imperial Formation in a
table.

Painted Hill Formation Allen (1957).

Palm Spring Formation Woodring (1931, 1932).

Split Mountain Forma- Tarbet in Tarbet and Holman
tion (1944) and Tarbet (1951)

Winker and Kidwell (1996) re-
interpreted some facies as the
Elephant Trees formation, in-
formal name, and included it
with other units (Garnet for-
mation, Red Rock [= Anza]
formation, and the Alverson
Volcanics) in the Split Moun-
tain Group.

Member ts a 60 m (200 ft) thick, locally-derived fossiliferous marine

sandstone in the lower part of the Imperial Formation. It overlies a
layer of coral rubble (the “reef’’ of early workers, or the oyster-
coral deposit near the head of lower Alverson Canyon of Kidwell,
1988: figs. 3, 4). Type section is in Fossil Canyon, southern Coyote
Mountains, Carrizo Mountain 7'2-minute quadrangle [Sec. 10, T 16
S, R 9 E]. Late Miocene to earliest Pliocene

Formation consists of more than 1,020 m (3,400 ft) of continental

pale-brown to light-gray, coarse-grained conglomerate and con-
glomeratic sandstone with clasts as large as 0.6 m (2 ft) in diame-
ter. The unit includes light-gray, coarse-grained cobble and pebble
lenses, discontinuous, distinctive, yellowish-brown, intercalated silt-
stones, and a basalt flow in the lower 300 m. Reworked marine
fossils from the underlying Imperial Formation are found in a silt-
stone bed and in channels in the conglomerates (Murphy, 1986).
Type area is east of Painted Hill in the Whitewater and Desert Hot
Springs 72-minute quadrangles. Originally regarded as Pliocene, it
is Late Miocene based on a dated olivine basalt with ages of 6.04
+ 0.18 and 5.94 + 0.18 Ma (J. L. Morton in Matti et al., 1985;
Matti and Morton, 1993). Microfossils from the shale lenses includ-
ed foraminifers from zones NI7—N19 and calcareous nannoplank-
ton from zones CN9-CNI1 of Bukry (McDougall e7 al., 1999: fig.
3, section WWX).

Formation is a 1.450 m (4.800 ft) thick, poorly-consolidated, brackish

to fluviatile, brown and red sandstone and claystone with abundant
lacustrine ostracodes (Quinn and Cronin, 1984). Type locality is at
Mountain Palm Spring (SW 4 Sec. 25, T 14S, R 9 E), near the
Old Carrizo Overland Stage site where Vallecito Creek joins Carri-
zo Wash, southern Vallecito Badlands, Arroyo Tapiado 72-minute
quadrangle. Originally considered Late Pliocene, but probably Early
Pleistocene based on vertebrates reported by Downs and White
(1967) and Downs and Woodard (1961) (Dibblee, 1996a,b).

Basal sedimentary unit of the southwestern Imperial basin includes a

400 m (1,300 ft) thick, nonmarine conglomerate and conglomeratic
sandstone with mostly tonalite boulders from the basement underly-
ing the Fish Creek Mountains. Kerr and Abbott (1996) regarded the
tonalite megabreccia exposed in Split Mountain Gorge as part of
the Split Mountain Formation and interpreted it as multiple sirz-
stroms or rock avalanche deposits. Type section is along Fish
Creek Wash where it cuts through Split Mountain Gorge [Sec. 36,
T 13. S,R8 E], Borrego Mountain, SE 742-minute quadrangle.
Miocene, older than the overlying microfossiliferous Late Miocene
Fish Creek Gypsum.

at Indio Hills, the south slopes of Garnet Hill, and
Willis Palm include Late Miocene and Pliocene facies,
based on megafossils and radiometric data (Rymer ef
al., 1994; Powell, 1988). None of the Imperial For-
mation fossils from the Salton Trough document a Ter-
tiary marine connection to the Pacific through southern
California marine basins, where penecontemporaneous
rocks mapped as the Castaic, Pico, and Monterey For-
mations contain temperate California margin faunules
(McDougall et al., 1999).

Painted Hill Formation, latest Miocene to Plio-
Allen (1957) gave this name to olivine basalts

cene.

and interbedded sediments northeast of Cabazon and
to all the continental beds that are conformable above
the Imperial Formation east of Painted Hill. The unit
constrains the youngest age of the Imperial Formation
in the Whitewater River section to 6.04 + 0.18 to 5.94
+ 0.18 Ma, the radiometric ages for a basalt flow in
the lower 300 m (J. L. Morton in Matti et al., 1985;
Matti and Morton, 1993) [see Table 6, herein, for the
sample location, which was published in a footnote to
a map]. Allen (1957) reported camel remains from the
Painted Hill Formation north of Cabazon and east of
Deep Canyon, but they were not age-diagnostic.

64 BULLETIN 371

Text-figure 39.—Imperial Formation in unnamed, south-flowing

tributary to Super Creek, east of the Whitewater River, northernmost
Salton Trough. Steeply dipping to overturned sediments of the Im-
perial Formation, including the basal ““worm tube-bed,”” overlie gra-
nitic basement. Patches of finer-grained sands (arrow) yielded ver-
tebrae and a mysticete (baleen whale) skull fragment (Thomas and
Barnes, 1993). The Banning strand of the San Andreas Fault Zone
is to the south (left). Two collectors (circled) for scale. Photo, E. C.
Wilson, 2002

Fish Creek/Vallecito basin
Plate 2, Column 22
(Text-figs. 38, 40, Table 6, Appendices 1, 2)

Column modified from Dibblee (1996b); area is
shown on the following 7!2-minute quadrangles: Harp-
er Flat, Borrego Mountain, Arroyo Tapiado, and Car-
rizo Mountain, California. See also the geologic maps
of Winker (1987) and Winker and Kidwell (1996).

Tertiary Stratigraphy

The Fish Creek/Vallecito Mountains area 1s under-
lain by late Cenozoic units as thick as 4,000 m (13,900
ft), including 1,000 m (3,300 ft) of exposed Imperial
Formation facies and a number of other units not pres-

ent at the Whitewater River area. The area south of

the Fish Creek Mountains and north of the Coyote
Mountains includes the Vallecito Badlands, the broad

valley of the Carrizo Creek, and the thickest accu-
mulation of sediments referred to the Imperial For-
mation. Kew (1914) described the Carrizo Creek for-
mation here, but his preoccupied name was replaced
by the Imperial Formation. Dibblee (1996b) again des-
... the most appropriate type sec-
tion” for the Late Miocene—Pliocene Imperial For-
mation.

ignated the area as *

Alverson Formation, Early to early Middle Mio-
cene.—The oldest Cenozoic unit here is the Alverson
Formation, which interfingers with the Split Mountain
Formation and is exposed along Fish Creek Wash. As-
sociated red beds underlie the volcanic unit in several
areas, including the southern Fish Creek Mountains
between Red Rock and Barrett Canyons and the south-
eastern Coyote Mountains between Fossil Canyon and
Painted Gorge. In its type area the Alverson Formation
contains an Early to Middle Miocene basalt and is con-
siderably older than the oldest known Imperial For-
mation. Winker and Kidwell (1996, and work in pro-
gress) preferred to rename the units below the Imperial
Formation in the Fish Creek-Split Mountain Gorge
area and place them in the Split Mountain Group.

Other names that have been used for the associated
redbeds are the Anza Formation, Red Rock formation,
and Miocene braided stream and alluvial fan deposits
of Kerr and Kidwell (1991). The beds are well-indu-
rated conglomerates and pebbly sandstones, coeval
with the basalts of the Alverson Formation (Text-fig.
40).

Split Mountain Formation in Split Mountain Gorge,
Miocene.—Dibblee (1996b) described the lithology of
up to 400 m (1,300 ft) of conglomerate that is cut by
Fish Creek Wash to form Split Mountain Gorge. Red-
dish alluvial conglomerates are overlain by rock slide
megabreccias of tonalite basement clasts, then by a
thin, brown, conglomeratic sandstone with claystones
that could also be included in the overlying Fish Creek
Gypsum.

Boulder beds with car-sized clasts are seen in spec-
tacular outcrop in Split Mountain Gorge. They have
been called the lower megabreccia, a member of the
Split Mountain Formation, landslide, and rock ava-
lanche deposits, but were identified by Kerr and Ab-
bott (1996) as two. sturzstroms, voluminous mass
transport deposits of shattered basement rocks that re-
sulted from successive events such as large magnitude
earthquakes. The lower sturzstrom is an older, red and
gray breccia; the upper megabreccia is the Split Moun-
tain sturzstom, a larger, tonalite deposit. Younger ma-
rine fan-delta mudstones and sandstones separate the
younger megabreccia from the overlying Fish Creek

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 65

Text-figure 40.—Split Mountain Gorge, Miocene reddish-brown

alluvial fan deposits exposed in Fish Creek Wash. View west at
rocks that Woodward (1974) referred to the Anza Formation (Bor-
rego Mountain SE 72-minute quadrangle SE ‘4, NW '%4 Sec. 25, T
13S, R 8 E). The alluvial sediments underlie the “lower boulder
beds,” which are now regarded as a sturzstrom in the Split Mountain
Formation (D. R. Kerr, written communication, 2004). Photo, J. C
Ingle, Jr., 1984

Gypsum, as seen on the geologic map by Kerr and
Abbott (1996).

Rapid movement of such massive deposits (hun-
dreds of millons of cubic meters) from adjacent moun-
tains to emplacement would have taken minutes, but
the time-frame for this catastrophic event can be esti-
mated from adjacent units. Kerr and Abbott (1996)
reviewed microfossil data from overlying marine sed-
iments and estimated that the rock fall and rapid flow
occurred at 5.4 + 0.3 Ma.

Fish Creek Gypsum, Late Miocene.—The Fish
Creek Gypsum, long regarded as a nonmarine evapo-
rite, has claystone intercalations that contain Late Mio-
cene, 9.5—7.5 Ma microfossils typical of a normal sa-
linity environment (Dean, 1996; McDougall, oral com-
munication, 1998). Peterson and Jefferson (1997) sug-

gested the gypsum could have been deposited near a
high-temperature hydrothermal vent. The deposits rep-
resent the second of three seawater incursions in the
northern ancient gulf, and the earliest seawater in the
Fish Creek Mountains area; they correlate with the
lower Imperial Formation section east of the White-
water River. Dean (1996) regarded the Fish Creek
Gypsum as a facies of the Imperial Formation because
both units are marine and have similar fossil assem-
blages.

A rock slide megabreccia of basement rock above
the Fish Creek Gypsum was called the upper fanglom-
erate by Woodward (1974), upper boulder bed by
Winker (1987), and upper breccia by Dean (1988).
Rightmer and Abbott (1996) named it the Fish Creek
sturzstrom and described its distinctive jig-saw puzzle
fabric and catastrophic Early Pliocene or latest Mio-
cene origin. It is the youngest of three such mass-trans-
port deposits exposed in Split Mountain Gorge.

Imperial) Formation in the Fish Creek/Vallecito
Mountains, Late Miocene—Pliocene.—Dibblee (1996b)
discussed the reasons why he proposed the Fish Creek
Mountains/Vallecito Badlands area as a new type sec-
tion for the Imperial Formation: it has the most com-
plete section, the maximum exposed thickness, and
both lower and upper contacts (conformable with the
underlying Split Mountain Formation and gradational
with the overlying fluviatile Palm Spring Formation).
Also, the earlier workers who first used the formation
name assumed but never clearly stated that Fossil Can-
yon was the type section.

The Imperial Formation in this area was most re-
cently mapped by Winker (1987) and Winker and Kid-
well (1986, 1996), who recognized a number of facies
as informal members based upon lithology and origin.
They termed locally derived marine units as ““L’-suite
sediments, and those transported by the ancient Col-
orado River as “C”*-suite sediments. The oldest Col-
orado River deposits are earliest Pliocene, found in the
upper part of their Wind Caves member, which was
dated by magnetostratigraphy as 4.3 Ma (Johnson et
al., 1983). Here as elsewhere in the Salton Trough,
Colorado River sediments are distinguished by mag-
netite-bearing sands and the presence of reworked Cre-
taceous microfossils from the Mancos Shale of the
Colorado Plateau (Gastil ef al., 1996).

Winker and Kidwell (1996) regarded the Imperial
Group as including the Latrania Formation, which they
further divided into six informal members, and the De-
guynos formation (informal name), which has four
members. Pending their publication of formal descrip-
tions, we use the earlier stratigraphic nomenclature of
Dibblee (1996b).

66 BULLETIN 371

The Barrett Canyon-Carrizo Impact Area in the Car-
rizo Mountain NE 72-minute quadrangle is not readily
accessible now, but it was mapped in 1904 by Men-
denhall (1910), who recorded the detrital coral layer
(termed a “reef’’) of the Imperial Formation above a
60 m (200 ft) thick lava flow at the head of Barrett
Canyon. He noted a stratigraphically lower sandstone
6-15 m (20—SO ft) thick on top of more lava flows.
Mendenhall (1910) wrote that the Fossil Canyon sec-
tion has only the upper part of this lowermost unit,
and that the Barrett Canyon section is more complete.

Quinn and Cronin (1984) sampled the lowest out-
crop of the middle Imperial Formation in Fish Creek
Wash and reported a diverse assemblage of foramini-
fers that McDougall er a/. (1999) noted were **. . . sim-
ilar to faunas found in the Late Miocene Imperial For-
mation near San Gorgonio Pass and very different
from faunas higher in the Fish Creek Wash section
which are clearly Pliocene.”” The upper section micro-
faunule in Fish Creek Wash consists mainly of the in-
tertidal to brackish foraminifer E/phidium gunteri Cole
(Quinn and Cronin, 1984).

Palm Spring Formation and Canebrake Conglom-
erate, Pliocene and Pleistocene.—Palm Spring For-
mation unconformably overlies the deltaic and shallow
tidal flat deposits of the upper Imperial Formation and
intertongues with the Canebrake Conglomerate to the
west.

Southern Coyote Mountains
Plate 2, Column 23
(Text-figs. 38, Table 6, Appendices 1, 2)

Column after Dibblee (1996b); the area is shown on
the Carrizo Mountain and Painted Gorge 72-minute
quadrangles, Imperial County, California.

Basement and pre-Imperial Formation rocks, Pa-
leozoic to Miocene.—Paleozoic metasediments form
the core of the Coyote Mountains; they are overlain
uncontormably by the Anza Formation, described
from the northern Coyote Mountains, and the Alverson
Formation, described from the southern Coyote Moun-
tains. The Miocene Alverson Formation is overlain by
the Miocene Split Mountain Formation, here a 100-m-
thick, unfossiliferous conglomerate (Dibblee, 1996b)
that is in turn unconformably overlain by the Imperial
Formation.

Imperial Formation, Miocene and Pliocene.—The
Imperial Formation crops out around the northern,
eastern, and southern flanks of the Coyote Mountains,
but the best known section is on the southern side
Where Hanna (1926) identified the lowest facies as a
basal “coral reef,” a well-indurated layer consisting of

broken coral fragments and other invertebrates. Pieces
of coral in this canyon caught the attention of the ear-
liest geologists, including Fairbanks (1893) and Men-
denhall (1910), who collected specimens that T. W.
Vaughan (1917) monographed; Vaughan recognized
their Caribbean affinities at once and termed them
“reef-corals,”” although they were collected from a de-
trital deposit, not a true reef.

The basal coral layer in Fossil Canyon is overlain
by a 650 m (200 ft) sandstone, the “*Latrania Sands,”
which Dibblee (1996b) interpreted as a thin marine
transgressive unit with abundant large echinoids. Kid-
well (1988) discussed details of the sands, which came
from a source to the south-southwest. She identified
shell beds in both upper and lower Alverson (also
known as Fossil or Shell) Canyon, and differentiated
fossil assemblages that correspond to changes in sed-
imentology. The Latrania Sand Member is covered by
very thick “Coyote Mountain Clays”; where they con-
tain oyster shell bioherms, as in the Yuha Basin, Hanna
(1926) called the facies **Yuha Reefs.”’ The claystone
member with sandstone and concentrations of oyster
shells is the equivalent of the middle muddy sandstone
member “Tim2” of Vazquez-Hernandez et al. (1996)
from the Sierra Cucupa and Laguna Salada basin.

Because the Imperial Formation in Fossil Canyon
was not given the name, complete description, and lo-
cality details that formalize a lithographic unit, Dib-
blee (1996b) designated a different type section in the
Vallecito Badlands southwest of the Fish Creek Moun-
tains.

Age and correlation of the Latrania Sand Member,
Imperial Formation, southern Coyote Mountains.—
Abundant megafossils were described from the La-
trania Sand Member (see Appendix 1), but its age re-
quires refinement. The Fossil Canyon outcrops are
possibly as young as the Early Pliocene predeltaic
Wind Caves member of Winker and Kidwell (1996) in
the Fish Creek/Vallecito Mountains (McDougall, oral
communication, 1999), but some of the megafossils
are Miocene.

Lyropecten tiburonensis Smith is found in Fossil
Canyon; a specimen from the Painted Gorge quadran-
gle [Section 5, T 16 S, R 10 E] had a *’Sr/*°Sr age of
5 Ma. It also occurs in the 12.9 Ma conglomerate of
Isla Tiburon with other Fossil Canyon mollusks such
as Turritella imperialis Hanna, Strombus obliteratus
Hanna, ““Aequipecten” plurinominis (Pilsbry and
Johnson), and Spondylus bostrychites Guppy of Hanna
(1926) [not of Guppy] (Gastil ef al., 1999). Most of
these are also found in Miocene units in the Boleo
basin and the southern Cabo Trough east of Santa An-
ita (J. T. Smith, 1991c).

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 67

The Latrania Sand Member has abundant large echi-
noids referred to the genera Clypeaster and Encope.
Kew (1914) illustrated Clypeaster bowersi Weaver
from Fossil Canyon, and J. T. Smith collected it from
Late Pliocene beds at Isla Cerralvo. The associated
mollusks are older than the echinoids, and the Late
Pliocene pectinids from Isla Cerralvo are missing in
the northern gulf. This suggests that the type section
of the Latrania Sand contains a mixed assemblage of
Miocene to Late Pliocene megafossils whose individ-
ual ages are not accurate for determining the age of
the formation in the southern Coyote Mountains.

Coral genera reported from the Imperial Formation
include Dichocoenia, Solenastrea, Meandrina, Sider-
astrea, and Porites (Vaughan, 1917; Kidwell, 1988).
All of the megafossil species from the southern Coyote
Mountains require a thorough taxonomic review that
reflects Tertiary-Caribbean nomenclature and a_ bio-
stratigraphic assessment, because many of the early
collections came from float and some seem to have
been reworked. For these reasons the Fossil Canyon
section might not be the best place for determining the
biostratigraphy of Imperial Formation species: many
of the same taxa are not reworked in Baja California,
Where they are associated with dated volcanic units.

Palm Spring Formation and Canebrake Conglom-
erate, Pliocene.—The upper Imperial Formation is
overlain by the Palm Spring Formation and the Cane-
brake Conglomerate, nonmarine clastic units that were
named for sections in the Coyote Mountains. They in-
tertongue in Carrizo Wash, north and west of the Coy-
ote Mountains, Palm Spring Formation to the east and
Canebrake Conglomerate to the west.

Cerro Prieto to Sierra Cucupa, Baja California
Plate 2, Column 24
(Text-figs. 38, 41, Table 6, Appendices 1, 2)

Column modified from Vazquez-Hernandez er al.
(1996); shown on the Sierra Cucapa quadrangle,
111D75, scale 1:50,000; and the geologic maps of Bar-

nard (1968), scale | inch represents | mile; and Muell-
er and Rockwell (1991).

Geographic Setting

The Salton Trough south of the international border
includes the Mexicali Valley, Laguna Salada basin, Si-
erra Cucupa [also spelled ““Cucapa”’], and the Sierra
Mayor. The northwest-trending Imperial and Cerro
Prieto Fault zones outline a spreading center in the
area of the Cerro Prieto geothermal field, which is un-
derlain by more than 5 km of deltaic and marine Neo-
gene sediments (Mueller and Rockwell, 1991). An ear-
ly incursion of the ancient Gulf of California is rep-

resented by rare, hydrothermally altered, poorly pre-
served, Middle Miocene, marine microfossils,
including Cassigerinella chipolensis (Cushman and
Ponton), in three samples from two deep wells in the
Cerro Prieto area (Cotton and Vonder Haar, 1979,
1980, 1981). Pliocene to Quaternary advances of the
gulf, the shifting Colorado River delta, and erosion of
the uplifted surrounding sierra contributed to the thick
basin sediments. Ostracods were the most common mi-
crofossils in cores from 185—1,952 m depths examined
by Ingle (1982); he interpreted a “significant mid-
Pleistocene marine incursion” from associated fora-
minifers and correlated the sediments with the Palm
Spring Formation.

The Laguna Salada basin is elongate, relatively wide
(10-20 km), and bounded by faults. Ongoing investi-
gations of the basin by Mueller and Rockwell (1991,
1995), Vazquez-Hernandez er al. (1996), Stock et al.
(1996), and Martin-Barajas er al. (2001) include data
from unpublished theses and geologic maps. Late Qua-
ternary uplift and the formation of stepped, en echelon
basins disrupted the sedimentary sequence and com-
plicate the interpretation of facies that have been fault-
ed, pulled apart, and deformed during subsidence.

Stratigraphic nomenclature and correlation of
marine deposits

Colonia Progreso volcanics, informal name, Middle
Miocene.—lsolated outcrops of the Colonia Progreso
volcanics of Barnard (1968) near the international bor-
der in western Mexicali are andesitic and dacitic brec-
cias of 15.3 + 0.8 Ma, but they are not in contact with
the younger Imperial Formation and do not constrain

its age.

Imperial Formation, Pliocene.—The Imperial For-
mation exposed in the Cerro Colorado Basin in south-
western Sierra Cucupa and northern Sierra Mayor has
three marine members—“Tim1],” **Tim2,.”* and
“Tim3”> described by Vazquez-Hernandez er al.
(1996)—that correlate with the upper claystone mem-
ber of the Imperial Formation in the southern Coyote
Mountains. In the Sierra Cucupa, basal member
“Timl” is a thin conglomerate and breccia layer in
low-angle fault contact with underlying Paleozoic
metamorphic and granitic basement rocks. It is over-
lain by “Tim2,” a mudstone, and “Tim3,”” a yellow-
beige, muddy sandstone.

The middle and upper members of the Imperial For-
mation in this area contain abundant, Pliocene, shal-
low-water, benthic microfossils (Wazquez-Hernandez
et al., 1996). Some are the same as those reported by
Cotton and Vonder Haar (1980) from Cerro Prieto.
Many occur with reworked Cretaceous foraminifers,

68 BULLETIN 371

calcareous nannofossils, and palynomorphs transport-
ed by the ancient Colorado River from the Colorado
Plateau to the prograding river delta.

Siem (1992) reported corals from the basal con-
glomerate-breccia facies,“Tim1” at “Coral Hill,” on
the eastern side of the Sierra Mayor (location shown
by Vazquez-Hernandez er al., 1996); E. C. Wilson
(written communication, 1991) identified specimens as
Dichocoenia sp. aff. D. merriami (Vaughan), a coral
that lived in a shallow-water, high-energy environ-
ment.

Coquinas of the fossil scallop Argopecten deserti
(Conrad), small oysters, mounds of Ostrea vespertina
of authors, and Anomia subcostata Conrad are com-
mon in the middle and upper members of the Imperial
Formation in the Sierra Cucupa and northern Sierra
Mayor. They could represent the impoverished faunule
of the last seawater incursion or an intermittent estu-
arine environment; Woodward (1974) regarded the
unit as Palm Spring rather than Imperial Formation.
The mollusks suggest correlation with younger Impe-
rial Formation facies in the Fish Creek/Vallecito Bad-
lands and similar coquinas in the upper beds of the
northern Loreto basin.

Nonmarine sediments, Quaternary.—The Imperial
Formation is separated by an unconformity from the
overlying Palm Spring Formation. It grades upward to
the Canon Rojo conglomerate, an informal name for
alluvial sediments in the western Sierra Cucupa and
northern Sierra el Mayor (Vazquez-Hernandez er al.,
1996: fig. 1). This area along the Laguna Salada offers
a unique opportunity to see Recent fault scarps in Ho-
locene sediments and a developing pull-apart basin
(Text-figs. 38, 41). One of a series of dilational right
steps is taking place where the northwest-southeast-
trending Laguna Salada Fault meets the northeast-
trending late Quaternary Canon Rojo Fault (Mueller
and Rockwell, 1991).

San Felipe embayment, Baja California
Plate 2, Column 25
(Text-figs. 1, 38, 42, Appendices 1, 2)

Column after R. L. Andersen (1973) and Boehm
(1982, 1984); area is shown on the Santa Clara quad-
rangle, H11B46, 1:50,000; and the geologic map of R.
L. Andersen (1973), scale 1:62,500.

Overview

The San Felipe embayment extends from northwest
of the port of San Felipe east and south of the southern
Sierra San Felipe (Text-fig. 2). The area includes 340
m of exposed Miocene and Pliocene marine sediments
representing bathyal to littoral depths (Boehm, 1984).

Text-figure 41

Canon Rojo area, western Sierra Cucupa, where

scarps of the northwest-striking Laguna Salada Fault and the north-
east-striking Canon Rojo Fault meet to form a corner of a pull-apart
basin (Mueller and Rockwell, 1991). Fault scarps are 3—4 m high;
Imperial Formation sediments to the south are Late Pliocene and
younger marine to estuarine facies with abundant Argopecten deserti
(Conrad), anomiids and oysters. Photo, J. T. Smith, 1990.

The units have undergone uplift, folding, and faulting
related to rifting in the Gulf Extensional Province
(Stock ef al., 1996).

P. V. Anderson (1993) named the prebatholithic
basement rocks the Playa San Felipe Group, which
includes eight informal formations described from
north of San Felipe. Those units were correlated pro-
visionally with Late Proterozoic and Early Cambrian
age rocks east of the Gulf of California in northwest-
ern Sonora, Mexico. In an earlier thesis, R. L. Ander-
sen (1973) reported andesite, basalt, and volcaniclastic
rocks of probable Miocene age and aeolian sandstone
of unknown age overlying the basement rocks. He also
mapped the Late Miocene and Pliocene marine se-
quence and illustrated a large assemblage of Neogene

megafossils.

Stratigraphy of Neogene marine units
west of San Felipe

Llano el Moreno Formation. Late Miocene.—The
formation and its two members were formally named
by Boehm (1984), who designated a composite type
section for the Llano el Moreno Formation. The sed-
iments crop Out approximately 25 km west-northwest
of the town of San Felipe along the eastern side of the
southern Sierra San Felipe, and 3—7 km north of the
unpaved road between Mexico 5 and Valle de San Fe-
lipe. Detailed geology and sample locations for this

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 69

part of the San Felipe quadrangle were presented by
Boehm (1982). The thickness of the marine section is
estimated as 100 m.

San Felipe Diatomite Member, Late Miocene—Early
Pliocene.
from exposures along the eastern side of the southern
Sierra San Felipe. The unit is more than 30 m thick
and contains Late Miocene, middle bathyal diatoms,

Boehm’s lower member was. described

silicoflagellates, radiolarians, and deep-water foramin-
ifers that suggest marine deposition in the embayment
began at 6.0—5.5 Ma. Most of the microfossils support
a Late Miocene age, but there are exceptions. The ra-
diolarian Didymocyrtis hughesi (Campbell and Clark)
has a last appearance datum of 8.6 Ma; it might have
been reworked from an earlier seawater incursion in
the northern gulf. Thalassiosira oestrupit (Ostenteld),
an Early Pliocene diatom zonal marker, and the radi-
olarians Didymocyrtis penultimus (Riedel) and Spon-
gaster pentas Riedel and Sanfilippo in the upper part
of the member suggest it is 3.6 Ma. The diatomite
member grades upward to the Canon las Cuevitas
Mudstone Member.

Canon las Cuevitas Mudstone Member, Late Mio-
The type section is exposed along an unpaved

Gene.
road just east of Buenavista Pass (Nelson, 1921), ap-
proximately 12—15 km west of Pete’s Camp on Mexico
5. The pumiceous mudstone is almost 65 m thick and
contains middle bathyal microfossils such as the Late
Miocene to Early Pliocene Uvigerina peregrina Cush-
man (Boehm, 1984, and revised ages for Zones N17—
N19). Stock (1997) reported a pumice and lapilli layer
just above the base that had a Ar/*°Ar age of 6.65 +
0.14 Ma.

Unnamed marine conglomerate, Pliocene.—The
overlying unnamed marine conglomerate of R. L. An-
dersen (1973) was referred to the Salada Formation by
Boehm (1984) and later authors, but that name is not
appropriate because of differences in lithology, prov-
enance, and age (see discussion of Arroyo Salada,
southern Magdalena Plain, p. 46). R. L. Andersen
(1973) estimated the composite thickness of the con-
glomerate as more than 250 m. The coarsely grained,
poorly sorted, shallow-water sandstone, distinguished
by cavernous weathering, crops out at “las Cuevitas”
(3.1 mi by odometer east of Buenavista Pass) and in
the southwestern Valle de San Felipe (Text-fig. 42). It
is a locally derived, granitic, beach deposit that over-
lies the mudstone with angular unconformity and con-
tains abundant internal molds of Pliocene mollusks.

Correlation
Megafossils in the unnamed marine conglomerate
are also found in the younger parts of the Imperial

Text-figure 42.—Unnamed granitic beach deposits northwest of

San Felipe contain internal molds of Pliocene mollusks. Outcrop is
12-15 km from Mexico 5 and approximately 750 m south of a local
landmark known as “‘Las Cuevitas.”” Photo, J. T. Smith, 1986.

Formation in the Fish Creek/Vallecito area of Califor-
nia, and in Early to Middle Pliocene sediments in the
southern Coyote Mountains. Exceptionally well pre-
served gigantic specimens of the Late Miocene—Early
Pliocene pectinid Euvola keepi (Arnold) are common
in the southernmost 15-m high ridge west of the road
after it turns south from the Buenavista Pass road.

Sierra de Santa Rosa
Plate 2 Column 26
(Text-fig. 38)

Column from Stock et al. (1996, 1999), after Bryant
(1986); area is shown on the Punta Estrella and Bahia
Santa Maria quadrangles, H11B57 and H11B67, re-
spectively, scale 1:50,000; and the geologic map of
Bryant (1986).

Stratigraphic Overview

The Sierra de Santa Rosa lie 20 km southwest of
San Felipe, betweeen the San Felipe and Puertecitos
marine embayments. The sierra represent a nonmarine
basin that contains an important marker bed, the Tuff
of San Felipe, which was described by Stock ef al.
(1999) from farther south.

Metamorphic and Cretaceous granitic to dioritic
basement rocks are unconformably overlain by a se-
quence of pre-Middle Miocene to Pliocene fluvial de-
posits and Miocene tuffs and basalts. Bryant (1986)
recognized three divisions of the Neogene clastic
rocks—Sequences 1, 2, and 3—which were further
subdivided by Stock er al. (1996). They distinguish a
lower arkosic sandstone overlain by conglomerate in
Sequence 1; Bryant’s Sequence 2 is a series of basalts
and pyroclastic flows ranging in age from 15 Ma to
8.9 Ma. Of these, the Tuff of San Felipe is the most

70 BULLETIN

extensive and significant for the history of the northern
Gulf of California. Sequence 3 consists of alluvial fan
deposits and fanglomerates.

Tuff of San Felipe, Middle Miocene.—Called
“Tmr,” by Bryant (1986), the Tuff of San Felipe was
named and described by Stock er al. (1999) for a wide-
spread, rhyolitic tuff that is well-exposed near Canon
el Parral between the Sierra de Santa Rosa and the
Sierra San Fermin (Text-fig. 43). It is characterized by
densely welded lithic lapilli and a thickness of 180 m
near its presumed vent area close to the present coast-
line. It has a radiometric age of 12.6 Ma and a low-
inclination reversed magnetization that was interpreted
by Stock er al. (1999) as within reversed polarity sub-
chron C5Ar.2r (12.401—12.678 Ma). The Tuff of San
Felipe extends over an 18,000 km? area, from the east-

ern side of the Sierra San Pedro Martir to the coast of

the Gulf of California and 40 km to the southwest.
Ongoing studies suggest the unit is present in Sonora,
providing a link between the eastern and western sides
of the ancient Gulf of California (Oskin ef al., 2000).

The Tuff of San Felipe is overlain by alluvial fan
deposits, younger tuffs, basalts dated at 8.9 + 1.2 Ma,
and Plio—Pleistocene continental deposits (Stock er al.,
1999).

Puertecitos embayment
Plate 2, Column 27
(Text-figs. 2, 43-45, Appendices 1, 2

Column after Martin-Barajas er al. (1997); the area
is shown on the Puertecitos quadrangle, H11B77, 1:
50,000; and geologic maps of Martin-Barajas er al.
(1995, 1997), Lewis (1994), and Stock er al. (1991)

Gec »graphic Setting

The Puertecitos embayment extends over approxi-
mately 300 km? from the southern Sierra San Fermin
to the fishing port of Puertecitos; it lies east of the
Sierra San Pedro Martir and the main Gulf escarpment.
Late Miocene to Early Pliocene shallow-water sedi-
ments dominate the section in the northern part of the
basin; volcanic units are more voluminous in_ the
south. The basin les north of most of the Puertecitos
Volcanic Province, which has a history of volcanism
from 21 Ma to 3 Ma, major pulses of activity at 6 Ma
and 3 Ma. The principal pyroclastic units are, oldest
to youngest: the Tuff of San Felipe, 12.6 Ma; the in-
formally named tuff of el Canelo, 6 Ma: two informal

units within the Puertecitos Formation, the tuff of

Mesa el Tabano, 5.9—3 Ma, and the tuff of Valle Cur-
bina, 3.27 Ma.

The region is the subject of a number of ongoing
investigations (Martin-Barajas et al., 1995; Lewis,

371

114° 50'W "EL Apache 71 ~~ ~~
ea ae creep Panett ‘sulfur mine

30°) +" +) +" Sierra’ + +
35'W ++ San Felipe’. ’

ae
es

3) Tuff of Mesa arte oe, Pe ae @O+-km
SS ei Tabano NP VR EAR 23

E=2] Puertecitos Fm. (> a Pc
Se Me km
(*] Tertiary volcanics Yay =r

Basement rocks
© Type section
~>\ Unpaved road
e = Town/village

A K/Ar age eae 0 10 KM
@ Megafossil locality —-=—=—

Text-figure 43
marine type sections. Regional map of northeastern Baja California

Puertecitos embayment, map showing Neogene

and the Puertecitos Volcanic Province (Tertiary volcanics symbol)
modified from Martin-Barajas er al. (1997) and Lewis (1996). Type
1, Tuff of San Felipe, late
Middle Miocene pyroclastic flows, 12.6 Ma, Canon el Parral; 2

sections of units described from the area:

Puertecitos Formation, Matomi Member, Late Miocene, composite
sections: 2, Arroyo la Cantera [also known as “Arroyo los Heme
Norte’’], 3, Valle Curbina: 4, 5, Puertecitos Formation, Delicias
Member, Early Pliocene, composite sections: 4, Campo Cristina
(CC), 5, Arroyo el Canelo, constrained by the Pliocene age of the
Tuff of Mesa el Tabano. SPME, Sierra San Pedro Martir Fault, west-
ern boundary of the Gulf Extensional Province. Only a few faults
are shown to indicate three major structural trends in strike in this
area: north-northwest, northeast, and northwest (Stock, 2000).

1996; Nagy er al., 1999, among others) because it is
key to the tectonic history of the Gulf Extensional
Province. The rocks record the transition from arc-vol-
canism to rift-volcanism and the Pliocene opening of
the Gulf of California (Martin-Barajas er al., 1995).
Text-figures 43 and 44 show principal locations.

Stratigraphy

Unnamed volcaniclastic rocks, pre-Middle Mio-
cene.—Pre-Cretaceous metamorphic and Cretaceous
granitic basement rocks are overlain unconformably by
volcaniclastic breccia and sedimentary rocks that were
intruded by young andesitic (?) dikes that have an Ar'?/

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 71

Text-figure 44.—Puertecitos Formation, view from south of Ar-

royo El Canelo toward Mesa el Tabano (dark rocks in lett back-
ground). A welded tuff, 5.9 + 0.2 Ma at its base and 3.1 + 0.5 at
its top, caps the mesa (Sommer and Garcia, 1970). Photo, J.T.
Smith, 1987.

Ar’ age of 8.6 + 0.5 Ma (Nagy, 1997). Another vol-
caniclastic breccia overlies the basement sequence and
has an Ar*°/Ar*? age of 15.5 + 0.5 to 16.1 + 0.5 Ma
(Stock ef al., 1999).

Tuff of San Felipe, Middle Miocene.—The Tutt of

San Felipe is a west-dipping, mesa-forming unit that
crops out over much of the western range front of the
southern Sierra San Felipe. It is a widespread, densely
welded, Middle Miocene, lithic-lapilli ash-flow deposit
that was identified and analyzed by Stock er al. (1999)
in several areas in northeastern Baja California. It
probably erupted from a vent north of the Sierra San
Fermin and east of the southern Sierra San Felipe. It
measures more than 100 m thick at its type section
near Canon el Parral, 2-3 km south of El Apache Sul-
phur Mine in the Bahia Santa Marta quadrangle (Lew-
is, 1994, 1996).

The tuff is an important marker bed that has dis-
tinctive petrographic and paleomagnetic characteris-
tics. It was labelled ““Tmr,”* on thesis maps of the
Santa Rosa Basin (Bryant, 1986) and in southern Valle
Chico (Stock, 1993). Detailed mapping of the inter-
vening Sierra San Fermin (Lewis, 1994, 1996) and Si-
erra Santa Isabel (Nagy er al., 1999), and other geo-
chronology and paleomagnetic studies by these authors
demonstrated that the same flow extends through all
the areas.

Stock er al. (1999) interpreted its age as approxi-
mately 12.6 Ma, based on Ar*’/Ar*’ determinations and
the ages of associated units. The tuff was also reported
east of the gulf in mainland Mexico; it is key to the
reconstruction of the Gulf Extensional Province, which
straddles the Pacific-North American Plate boundary
(Oskin er al., 2000).

Tuff of El Canelo, informal name, Late Miocene.—
The Late Miocene ignimbrites known informally as

the tuff of El Canelo of Martin-Barajas et al. (1995)
and another rhyolite flow rest unconformably on a vol-
caniclastic breccia in the area of Arroyo el Canelo,
which drains to the northeast from Mesa el Tabano
(Text-fig. 44). The age of the tuff of El Canelo is 6.4
+ 0.02 Ma (Martin-Barajas er al., 1997). It includes
three lithologic units: an unwelded lithic lapilli tuff, a
densely welded lithic, crystal-, and lapilli-rich tuff, and
a non- to partly-welded lithic and pumice tuff contain-
ing large landslide blocks (Lewis, 1996). This unit is
unconformably overlain by a marine sedimentary se-
quence.

Puertecitos Formation, Late Miocene—Late Plio-
cene.—Martin-Barajas et al. (1997) named the Puer-
tecitos Formation for a type section 5 km northwest
of Puertecitos in the quadrangle of the same name (see
also Martin-Barajas ef al., 1993). The formation con-
sists of two westward-thinning, wedge-shaped, trans-
gressive-regressive, shallow-water, marine sequences:
the Matomi Mudstone Member, which interfingers
with pyroclastic deposits mapped as ‘*Ptb” by Stock
et al. (1996), and the younger Delicias Sandstone
Member (**Ptg” of Stock et al., 1991). The two mem-
bers are separated by an angular unconformity in the
north; in the south they are divided by a pyroclastic
unit, the tuff of Valle Curbina, dated at 3.27 + 0.04
Ma (Martin-Barajas et al., 1997). Other volcaniclastic
units are included in the upper part of the Puertecitos
Formation.

Matomt Mudstone Member, Late Miocene—Early
Pliocene.—The type locality of the Matomr Mudstone
Member is a composite section exposed along the
range front bordering an alluvial plain 5 km northwest
of Puertecitos. It crops out in two adjacent valleys,
Valle Curbina and Arroyo la Cantera (= Arroyo los
Heme Norte of Stock et al. (1991), who mapped the
unit as “Pmy’’). Martin-Barajas et al. (1997) named
the mustard-colored shallow marine unit, which con-
tains oyster biostromes, abundant bivalve molds, and
a turritellid that to date is unique in west Mexico (Text-
fig. 45). The Matomr Mudstone is probably Late Mio-
cene in age; it overlies and pinches out against a 5.8
+ 0.5 Ma rhyolite dome on the western side of Valle
Curbina (Martin-Barayas ef al., 1995, 1997), At El Co-
loradito, east of the Sierra San Fermin, the basal con-
glomerate overlies a 6.5 Ma rhyolite tuff (Lewis,
1996). In Valle Curbina the sediments are 35 m thick
and grade upsection to a coarse-grained fossiliferous
sandstone and pebble conglomerate. Megafossils from
this member in Arroyo el Canelo were dated by R. E.
Denison, then of Mobil Oil Company, using *’Sr/*°Sr
analyses; the ages were interpreted as Late Miocene

72 BULLETIN 371

Text-figure 45.—Matomr Mudstone Member, west of the road

trom San Felipe to Puertecitos. Between Arroyo Matomi and Arroyo
El Canelo, the mustard-colored beds contain large, double-valved
oysters with distinctive radial furrows: the sediments are overlain by
a 2-m ash bed and terrace deposits. Photo, J. T. Smith, 1987

and latest Middle Miocene (Gastil ef al/., 1999: table
dys

Delicias Sandstone Member, Pliocene.—The stra-
totype for the Delicias Sandstone Member is a com-
posite of sections exposed along the southern and east-
ern front of the Sierra San Fermin in the Puertecitos
quadrangle. It is Pliocene in age, the lower part crop-
ping out in a hill north of Arroyo el Canelo and the
upper part forming marine terraces at Campo Cristina,
S00 m south of the San Felipe—Puertecitos road be-
tween km 57 and the gulf. Fossiliterous muddy sand-
stones alternate with sandstone-siltstone beds, re-
worked ash-lapilli, and bentonitic layers; coarser ma-
rine deposits cap the section in Valle Curbina, where
it is unconformably overlain by alluvial conglomerate.
The member is not correlative with the earlier named
Early to Middle Eocene Delicias Formation of the Ti-
juana basin (Flynn, 1970).

Martin-Barajas er al. (1997) regard the lower section
of the Delicias Sandstone Member as time-transgres-
sive; the upper part of the unit interfingers with several
distinct pyroclastic deposits.

Tuffs associated with the upper Puertecitos For-
mation, informal names of Stock et al. (1996), Early
to Late Pliocene.

Extrusive volcanic units, including

the tuff of Valle Curbina, informal name, are interbed-
ded with or overlie the Puertecitos Formation. They
include pyroclastic deposits shown on the maps by
Stock et al. (1996) and in our column for the Puerte-
citos embayment as “Ptb” (dark gray lithic tuff),
“Pte” (white, crystal-rich pumiceous tuff) and “Ptf”’
(reworked air-fall deposits). “Pte” is a reworked green
tuff in the upper part of the Delicias Sandstone Mem-
ber. The flat-lying welded tuff of Mesa el Tabano, in-
formal name, caps the mesa west of Arroyo El Canelo
(Text-fig. 44). Sommer and Garcia (1970) reported K/
Ar dates of 5.9 + 0.2 Ma and 3.1 + 0.5 Ma for the
base and top, respectively, of this unit; Martin-Barajas
et al. (1995) obtained an Ar*’/Ar*’ age of 3.08 + 0.04
Ma for the same tuff.

Correlation

The Puertecitos Formation has not been recognized
outside of the Puertecitos area except for a dredged
sample from east-northeast of Isla San Lorenzo, one
of the Midriff Islands 240 km to the south (28°37.0'
N, 112°43.2" W, Natural History Museum of Los An-
eles County Invertebrate Paleontology locality
2542) (Text-fig. 46). Correlation of the Puertecitos
Formation is complicated by a great variety of marine
facies that include intertidal mudstone, fine-grained
sandstone, conglomeratic sandstone, and colluvium.
Molluscan fossils from the lower Matomi Mudstone
Member, including the Miocene Panamic pectinid
Amusium toulae (Brown and Pilsbry) and the epitoniid
gastropod Amaea (Scalina) edwilsoni DuShane, are
also found in the Late Miocene to Middle Phocene
Tirabuzon Formation of the Boleo basin.

Bahia de Guadalupe to Bahta las Animas
Plate 2, Columns 28, 29, 30
(Text-figs. 2, 46, Appendices 1, 2)

Column 28 modified from Parkin (1998). The Gua-
dalupe Basin is shown on the Campo Juarez quadran-
gle, HI2C42, 1:50,000; and the geologic maps of Gas-
til et al. (1975), scale 1:250,000, and Parkin (1998),
scale 1:10,000; Bahia de los Angeles and Bahia las
Animas are shown on the Bahia de los Angeles quad-
rangle, H12C52, scale 1:50,000.

Geographic Setting

The area from Bahia de Guadalupe to Bahta de las
Animas lies west and south of Isla Angel de la Guarda
and the Canal de Ballenas, west of the boundary be-
tween the Pacific and North American Plates marked
by the Ballenas, Partida, and San Lorenzo Fault Zones.
Although many lithologic units are not yet formally
described, ongoing and recently completed studies in-
dicate that the region contains marine sediments as-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 73

mw, 1s KG!

Cait angeles % 3s 29° N
Bal 10s Ang D ~ A3s a
e\0". Bi Isla |

Tiburon /
@

Isla San
Esteban

ZU
5
Oo
3
3
E
Vv
nm

Beomaea
N
\

-) Bahia

J \ de San Rafael

{

. El Barril
e = Town/village & \

/~~ Unpaved road
@® Microfossil locality

@ Megafossil locality
& Ar/Ar age locality

Text-figure 46.—Bahia de Guadalupe to El Barril, map including
Isla Angel de la Guarda. #Ar/’Ar ages (Delgado-Argote er al.
2000a): ash-flow tuff west of Bahia de los Angeles, 14.2 + 0.1 Ma;
basalt, northern Sierra las Flores, 12.1 + 0.1 Ma). Megatossils:
A-numbers and Islas San Lorenzo localities are from University of
California, Berkeley, Museum of Paleontology collections (Durham,
1950). Rocks dredged from 200 m at 28°37.0' N, 112°43.2' W [Nat-
ural History Museum ot Los Angeles County, Paleobiology De-
partment locality LACMIP 12542] have the same lithology and me-
gafossils as the Puertecitos Formation, Matomi Member. 8SEB: En-
senada Blanca area fossil locality of D. and J. Cox, 1988. Sources
of data for other fossil localities: southwestern Isla Tiburon, Gastil
et al. (1999); Isla San Esteban, Desonie (1992); Bahia de Guadalupe
to Ensenada Alcatraz, Parkin (1998), G. Axen and M., Tellez-Duarte
field collections; Sierra las Flores and Sierra las Animas, Delgado-
Argote et al. (2000a). EA, Ensenada Alcatraz; PA, Punta de las
Animas; PR, Punta Remedios: PS, Punta Soledad; PSE Punta San
Francisquito.

sociated with datable volcanic rocks that can provide
further important details on the geologic history of this
part of the Gulf Extensional Province. Prior to Plio-
cene time, Isla Angel de la Guarda and the San Lor-
enzo Islands were part of the Baja California peninsula
(Delgado-Argote ef al., 2000b). These islands moved
southeast as a rigid block along the San Lorenzo and
Partida Faults (Escalona-Alcazar et al., 2001).

The Guadalupe Basin extends over 50 km’, from
approximately 29°15’ N, 113°40' W to west of Ensen-

ada Alcatraz. Its rocks are younger than those in the
embayments to the south, where the record of Early to
late Middle Miocene volcanic rocks and Late Pliocene
fossiliferous marine sediments is more extensive (Par-
kin, 1998; Delgado-Argote et al., 2000a,b).

Stratigraphy

Pre-Cenozoic basement rocks.—Cretaceous granit-
oid rocks that intruded Paleozoic metasediments and
Mesozoic sandstones and shales have K/Ar ages of 99
Ma and 91.5 Ma (Delgado-Argote et al., 1997; Rom-
ero-Espejel and Delgado-Argote, 1997). They are
overlain unconformably by a sequence of volcanic
units, sandstones, conglomerates, and alluvial and la-
custrine deposits.

Unnamed Miocene sediments and volcanic debris-

flow deposits.—The oldest Tertiary unit in the Gua-

dalupe Basin is a pink biotite-rich, poorly welded tuff
that has an Ar*®/Ar*? age of 22.6 + 0.4 Ma (Parkin,
1998). It is discontinuous and separated by unconfor-
mities from both overlying and underlying rocks. In
the western part of the basin volcanic debris-flow de-
posits contain isolated packages of 8—15 m thick lime-
stone coquina and siltstone interbeds; they are overlain
by younger green debris-flow deposits (Parkin, 1998).

Andesitic lava flows of 17 and 18 Ma were reported
by Delgado-Argote er al. (1997, 2000a) from Isla An-
gel de la Guarda and Bahta de los Angeles. To the
west Middle Miocene pyroclastic flows and basaltic
andesites comprise three parallel ranges, thickening
east to west: the Sierra las Animas, Sierra las Flores,
and Sierra la Libertad. Dacitic to rhyolitic rocks have
Ar’/Ar® ages of 14 + 0.1 and 12.1 + 0.1 Ma, re-
spectively (Delgado-Argote et al., 2000a). Associated
fossiliferous marine sediments in the Sierra las Animas
are interpreted by Delgado-Argote er al. (2000a,b) as
Middle Miocene marine deposits of the ancestral Gulf
of California; they illustrate internal molds of Dosinia
and Glycymeris from Canada la Tinaja, western side
of Cerro Las Tinajas in the Sierra Las Animas.

West of Bahia las Animas the marine sequence is
overlain by volcanic debris-flow and pyroclastic de-
posits of 5 + 1.0 Ma and 3.8 + 0.3 Ma (Delgado-
Argote ef al., 2000a) and by Quaternary beach and
fluvial sediments (Parkin, 1998).

Unnamed marine sediments near El Barril, Plio-
cene.—Unnamed fine- to medium-grained, mustard
brown, friable sandstones and limy gray concretions
with fossil molds are associated with volcaniclastic
breccias approximately 2 km south of Punta San Fran-
cisquito and north of El Barril in the El Barril quad-
rangle. Dennis and June Cox made reconnaissance col-
lections of Late Pliocene marine megafossils in 1988

74 BULLETIN 371

from an unnamed coquina in Arroyo Ensenada Blanca.
The fossils included abundant oysters, coralline algae,
and internal molds of gastropods, as well as the pec-
tinid index species Argopecten abietis (Jordan and
Hertlein), Argopecten revellei (Durham), “‘Aequipec-
ten” corteziana (Durham), and the sand dollar Encope
shepherdi Durham.

The unit corresponds to the unnamed marine sedi-
ments west of San Felipe, the Carmen-Marquer For-
mation, undifferentiated, of the Loreto embayment,
and marine units in the Islas Tres Martas and Isla Cer-
ralvo. The pectinids and the sand dollar Encope shep-
herdi Durham correlate fossiliferous sandy siltstones
in the Guadalupe basin with unnamed marine beds on
the southeastern part of Isla Angel de la Guarda, Isla
las Animas of the San Lorenzo archipelago (Durham,
1950), and the eastern side of Isla San Esteban (De-
sonie, 1992) (Text-fig. 46).

San Lorenzo Archipelago
Plate 2, Column 31
(Text-fig. 46)

Column from Escalona-Alcazar ef al. (2001); the
area is shown on the geologic map by Gast er al.
(1975), scale 1:250,000; and by Durham (1950: fig.
14).

Geographic Setting

The San Lorenzo Archipelago is 27 km long and
includes Isla San Lorenzo and Isla Animas, approxi-
mately 20 km northeast of Bahta San Rafael. The ex-
posed sequence correlates with a section on the eastern
side of the Sierra las Animas (Delgado-Argote and
Garcia-Abdeslem, 1999).

Stratigraphy

Crystalline basement in the central and southern part
of Isla San Lorenzo consists of Paleozoic (?) green-
schist facies metamorphic rocks and a tonalite pluton.
It is unconformably overlain by a sequence of Neo-
gene marine sandstone, conglomerate, and gypsum
overlain by subaerial Pliocene andesitic lavas, lapilli-
rich crystalline tuff, brecciated lithic tuff, and pumice.
Quaternary alluvium and beach deposits cap the sec-
tion.

Unnamed marine sediments, Late Pliocene.—Dur-
ham (1950) collected Late Pliocene megafossils from
a section on the western side of Isla las Animas (his
“North Island,” University of California, Berkeley,
Museum of Paleontology locality A-3594). Specimens
occurred in well-bedded, northwest-dipping, coarse

sandstone deposits overlain by conglomerates and vol-
canic rocks. Molluscan taxa included Euvola keepi

(Arnold), Argopecten deserti Conrad, Argopecten re-
vellei (Durham), and Ostrea vespertina Conrad.

Correlation

Contemporaneous sedimentary and volcanic activity
has continued since the Miocene in the northern Gulf
of California, as seen from similar volcano-sedimen-
tary sequences at San Felipe, Puertecitos, Isla Angel
de la Guarda, Bahia de los Angeles, Isla Tiburén, and
Isla San Esteban (Escalona-Alcazar et al., 2001). The
Isla las Animas taxa include common index species
found from the Islas Tres Marias to Bahta de Guada-
lupe and the younger sections of the Imperial Forma-
tion.

Southwestern Isla Tibur6n, Sonora
Plate 2, Column 32
(Text-figs. 1, 2, 46, 47, 48, Appendix 1)

Column trom Gastil ef al. (1999), Geologic map,
Gastil et al. (1999), scale 1:250,000, and Oskin and
Stock (2003), scale 1:50,000.

Geographic Setting

Isla Tiburon, the largest island in the Gulf of Cali-
fornia, lies at approximately 29° N, 112°30' W, east of
the boundary between the North American and Pacific
Plates and within the area of the southern Basin and
Range Province. It is 10-20 km offshore from Bahia
Kino and Puerto Lobos, Sonora, Mexico. The north-
west to southeast-trending la Cruz Fault can be traced
on the northern side of the feature informally known
as “Cerro Starship” (Text-fig. 47).

Mapped by Gordon Gastil and students from 1983—
1987, the southwestern part of Isla Tiburon includes
almost 3 km of stratified Early Miocene to Quaternary
volcanic and sedimentary rocks that record the geo-
logic history of this part of the ancient gulf (Gastil er
al., 1999). Rocks older than 9-11 Ma are tilted; those
younger than 9 Ma are generally horizontal. A key unit
is a distinctive marine conglomerate, unit M8 of Gastil
et al. (1999), which has not been identified west of the
Pacific/North American Plate boundary. It is older and
thicker than the sequences at Islas Tres Martas near
the mouth of the Gulf of California (McCloy ef al.,
1988). Pleistocene marine terrace deposits are found
near Punta Willard on the southwestern part of the
island.

Stratigraphy

Basement rocks and pre-Miocene sedimentary and
volcanic units.—Continental redbeds, chert, and car-
bonate rocks overlie Cretaceous granodiorite and ton-
alite basement. They are intercalated with or overlain
by Miocene volcanic rocks 22—14 Ma in age and by

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 75

|
112° 30.6' W
4 K-Ar locality

&_ microfossils

@ megafossils

Bahia
Vaporeta

Ensenada Blanca

Text-figure 47.—Southwestern Isla Tiburon, Sonora, locality map
modified from Smith (1991c).

Middle to Late Miocene andesites, dacites, and rhyo-
lites between 13 Ma and 9 Ma that are interbedded
with or unconformably overlie the marine conglom-
erate. All units bear informal lithostratigraphic desig-
nations rather than formal formation names (Gastil e7
al., 1999).

Unnamed volcanic rocks, Units M1—M7 of Gastil et
al. (1999), Early and Middle Miocene.—The volcanic
units, part of the magmatic are that existed from 24 to
11 Ma in the area of the present Gulf of California,
were studied by Neuhaus (1989a,b) and Neuhaus ef al.
(1988). They include andesitic flows and breccias of
22.7—18.8 Ma, tufts, flows, and breccias of 14.9—20.5
Ma; they are designated Units MI—M7 as detailed by
Gastil et al. (1999), who reported radiometric dates for
22 samples. These ages fall within the 24—11 Ma range
published for volcanic rocks in the Sierra Santa Ursula
east of Guaymas, Sonora (Mora-Alvarez and McDow-
ell, 2000).

Unnamed conglomerate and sandstone, Unit MS of

Gastil et al. (1999), Miocene to Early Pliocene.—The
primarily marine sandstone and pebble to cobble and
boulder conglomerate is a unique 1,500-m-thick unit

Miocene volcanic breccia, southwestern Isla Ti-

Text-figure 48
buron. Gastil et al. (1999) reported a K/Ar age of 12.9 + 0.4 Ma
for a monomict breccia interbedded with marine conglomerate in
“Arroyo 3” (sample 83BSJ260). Photo, J. G. Smith, 1983; area of

photograph approximately 0.8 m across.

that crops out over an 8 km? area. It is exposed in
several northwest-trending arroyos that cut perpendic-
ular to the strike of the beds and empty into Bahta
Vaporeta, 3—4 km northeast of Punta Willard. Cassidy
(1989) measured sections and investigated the primar-
ily volcanic clasts and silt to coarse sand sediments,
which dip 15° to 25° to the northwest. Gastil er al.
(1999) recognized four facies of sandstone and con-
glomerate, Units M8a through M&d, of which Unit
M&d contains the highest concentration of marine me-
gatossils.

The marine conglomerate was deposited on consid-
erable topographic relief over volcanic rocks dated at
15—17.6 Ma. Its late Middle or earliest Late Miocene
age is based on a 5- to 1-m-thick monolithologic vol-
canic debris-flow deposit exposed in the floor of the
south branch of “Arroyo 3” (Text-fig. 48). The deposit
has a K/Ar age of 12.9 + 0.4 Ma (J. G. Smith in J. T.
Smith et al., 1985). Sampled before a topographic base
map and GPS were available, its coordinates were de-
termined as accurately as possible as 28°53.7' N,
112°30.6' W; the outcrop was not seen by Oskin and
Stock (2003: M. Oskin, oral communication, 2003).
The marine conglomerate 1s overlain with angular un-
conformity by an ash-flow tuff and dikes that cap Cer-
ro Starship (Unit M9 of Gastil ef al., 1999).

Megafossils from Unit M8 represent faunules from
several habitats, the most important of which is a shal-
low neritic assemblage of articulated pectinids that
were buried alive and are now well exposed in the
section near the mouth of “Arroyo 4,” locality 3 of
Gastil ef al. (1999). Many of the taxa have strong Ter-

76 BULLETIN 371

tiary Caribbean affinities, in contrast to the endemic
younger Gulf of California assemblages that evolved
in the Pliocene. Representative species include Argo-
pecten demiurgus (Dall), “Aequipecten” muscosus
(Wood) or an ancestral subspecies, Lyropecten tibu-
ronensis Smith, Strombus obliteratus Hanna, Strombus
(Tricornis) sp. cf. S. (7.) galeatus (Swainson), Turri-
tella sp. cf. T. umperialis Hanna, and species of Eu-
vola, Flabellipecten, Spondylus, and Atrina under re-
view by J. T. Smith.

A white sandstone facies mapped as Unit M&c crops
out upsection from the debris-flow deposit in “Arroyo
3°; it has few megatossils and its inner to outer neritic
(SO—150 m) microfossils suggest that the facies is Late
Miocene to Early Pliocene, no older than 6.5 Ma (In-
gle in Gastil et al., 1999, who also reported on samples
from earlier reconnaissance studies by Weaver, 1979,
1981). Ingle listed planktonic species from Planktonic
Foraminiferal Zones N1I7B to N19 (6.4 Ma—4 Ma).
Benthic species range from Miocene to Recent; many
currently live in the Gulf of California. The exception
is Amphistegina gibbosa d’Orbigny, a tropical shal-
low-water species that ranges from Miocene to Holo-
cene in the Caribbean; it lived only from latest Mio-
cene to Early Pliocene, no later than 4.3 Ma, in the
early Gulf of California and Pacific Ocean (McDougall
et al., 1999). Amphistegina gibbosa d Orbigny is also
reported from a Late Miocene (6.5—6.04 Ma) section
of the Imperial Formation in the northernmost Salton
Trough (McDougall et a/., 1999) and in the Fish Creek
and Vallecito Mountains (Ingle, 1974; Quinn and Cro-
nin, 1984), from Isla Carmen (Natland, 1950, as Am-
phistegina sp.), and trom Early Pliocene sediments at
Isla Marta Madre (McCloy er al., 1988). Calcareous
nannofossils listed from Isla Tiburon suggest “*... an
age close to the Miocene—Pliocene boundary . . .”’ (In-
gle in Gastil et al., 1999).

Ingle in Gastil et al. (1999) also included compar-
ative data for microfossils from Punta Mita, Nayarit,
and he listed species common to Isla Tibur6n and the
“Santiago diatomite” of the Cabo Trough. Tropical-
subtropical, latest Miocene to Early Pliocene foramin-
ifers from the white sandstone facies at Isla Tibur6n
are different from and younger than more temperate,
early Late Miocene, outer neritic taxa from Punta
Mita, north of Puerto Vallarta; there unnamed micro-
fossiliferous siltstones are intercalated with or imme-
diately underlain by volcanic rocks with K/Ar ages of
10.2 and 11.1 Ma (Jensky, 1975; Gastil et al., 1978).

Gastil et al. (1999) acknowledged but were not able
to explain the discrepancy between radiometric and
megafossil ages and those from micropaleontology.
They did not observe relationships between facies,

possible faults or other aspects that could resolve these
differences.

Oskin and Stock (2003) estimated that the marine
conglomerate is considerably thinner than originally
described, and that foreset beds were repeated by
slumping and landslides. They also favored the youn-
ger age of the microfossils for the entire section and
a marine origin concurrent with Pliocene spreading
and en echelon faulting.

Ash-flow tuffs and rhyolite flows, Units M9-M11 of
Gastil et al. (1999), Late Miocene to Pliocene.—The
tilted marine conglomerate of Unit M8 is separated by
an angular unconformity from Units M9—M11, which
include flat-lying ash-flow tuffs dated at 11.2 + 1.3 by
Gastil and Krummenacher (1975, 1977), rhyolite flows
and Early Phocene dikes that cap Cerro Starship. The
dikes yielded ages of 4.16 + 1.8 Ma and 5.67 + 0.17
Ma (Gastil et al., 1999); Oskin and Stock (2003) re-
determined the capping unit as feeder dikes of 5.7 =
0.2 Ma.

Implications of the section at southwestern Isla Ti-
buron for the history of the ancient gulf-—The Mio-
cene marine conglomerate and interbedded 12.9 Ma
debris-flow deposit pre-date by almost 8 Ma the sea-
floor spreading and oblique rifting that occurred be-
tween 3 Ma and 5 Ma at the mouth of the Gulf of
California (Larson, 1972). The section at southwestern
Isla Tiburon is unique in lithology and thickness, al-
though some of the same megafossils are found in re-
worked Late Miocene sediments of the lower part of
the Imperial Formation near the Whitewater River, and
in the southern Coyote Mountains, the Boleo basin at
Santa Rosalia, and unnamed sediments east of Santa
Anita in the southern San José del Cabo Trough. Re-
worked late Middle Miocene microfossils were re-
ported from younger units in the northernmost Salton
Trough (McDougall et a/., 1999), Yuma basin (Mattick
et al., 1973; P. B. Smith in Lucchita, 1972), Cerro
Prieto geothermal field (Cotton and Vonder Haar,
1979, 1980, 1981), and subsurface cores from Sonora
(Lozano-Romen, 1975; Gomez-Ponce, 1971: King,
1939). These records suggest an earliest incursion of
seawater in the northern gulf area by 12—13 Ma, and
provide evidence of the Miocene protogulf of Fenby
and Gastil (1991) that was proposed for the area be-
tween the Sierra Madre Occidental and the eastern
shore of the modern gulf. The megafossils from Isla
Tiburon include live-buried assemblages, whereas the
other evidence comes from reworked late Middle Mio-
cene taxa associated with Late Miocene or younger
marine sediments.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH Td:

Isla San Esteban
Plate 2, Column 33
(Text-fig. 46, Appendix 1)

Column is from Desonie (1992), who also published
a reconnaissance geologic map, scale | cm represents
0.4 km.

Isla San Esteban is primarily a calc-alkaline volca-
nic island in a zone of active rifting approximately 15
km southwest of Isla Tibur6n. Desonie (1992) mapped
an area of marine fossiliferous sandstone near the
mouth of a major west to east drainage known as Ar-
royo Limantour. She reported a dacitic flow below the
marine rocks with a radiometric age of 2.77 + 0.05
Ma. Megatfossils from this sandstone include the com-
mon Late Pliocene index species Argopecten abietis
(Jordan and Hertlein) and other taxa that correlate the
rocks with the Carmen-Marquer Formation, undiffer-
entiated, in the Loreto embayment, the Infierno For-
mation at Santa Rosalia, and unnamed sediments at
Bahia de Guadalupe, Isla Cerralvo, and the Islas Tres
Marias.

Boleo Basin
Plate 2, Column 34
(Text-figs. 2, 49, 55, Appendices 1, 2)

Column modified from Touwaide (1930), I. FE Wil-
son (1948), and I. F Wilson and V. S. Rocha (1955).
Area is shown on the Santa Agueda, Santa Rosalia and
Punta Santa Ana quadrangles, G12A35, G12A36 and
G12A25, respectively, 1:50,000. Geologic maps are
included in I. F Wilson (1948), I. F Wilson and M.
Veytia (1949), I. EF Wilson and V. S. Rocha (1955),
and Holt er al. (2000).

Overview

The Boleo basin lies along the central Gulf of Cal-
ifornia, south of Caldera La Reforma and east of the
Sierra Santa Lucta. It could extend as far south as the
northern tip of the Concepcion Peninsula. The basin
includes the 33 km* Boleo Copper District, mined
from 1885 to 1947 by the Compagnie du Boleo, and
the Lucifer Manganese District, 12 km northwest of
Santa Rosalia (I. EF Wilson and M. Veytia, 1949). Its
western edge is obscured by Tertiary volcanic arc
rocks of the Sierra Santa Lucia (Sawlan and J. G.
Smith, 1984). A number of east-flowing arroyos with
names such as Arroyo Purgatorio and Arroyo Infierno
expose the section (Text-figs. 49, 55).

The area is critical for documenting the time-strati-
graphic framework of the tectonic history of the cen-
tral Gulf of California and its volcanic arc. More than
500 m of volcanic rocks, 600 m of marine sediments,
and numerous uncontormities record the Neogene vol-
canic and depositional history of the basin from 24

Volcan ,
el Azufre/* ) Cerro
z J la Reforma
Volcan las * § t
Virgenes\__/
Esperanza

Isla San
Marcos
pn

(ee
\

lsan Lucas Le
san Brun

Rancho
Town/village
K/Ar locality
Mexico highway |
Megafossil locality

Microwave tower Caguama 2

Text-figure 49.—Tres Virgenes to Santa Rosalia, B.C.S., index
map to the Boleo basin and surrounding area. Sawlan and J. G.
Smith (1984) reported a K/Ar age of 10.1 + 0.4 Ma for a subaerial
tholeiitic flow in the basalt of Rancho Esperanza north of Rancho
Mezquital (27°25.36' N, 112°34.05’ W). Late Pliocene fossils from
Isla San Marcos discussed by Anderson (1950: fig. 11) and Durham
(1950) are deposited in the University of California, Berkeley, Mu-
seum of Paleontology collections.

Ma to | Ma. Sawlan (1991) discussed the geochem-
istry of the volcanic rocks through time. The earliest
seawater entered the Boleo basin in the late Middle
Miocene to early Late Miocene, as seen from shallow-
water assemblages of Tertiary-Caribbean fossils
draped over a submerged dome that has a K/Ar age of
approximately 12 Ma (J. T. Smith, 1991b,c) (Text-fig.
50).

The origin of secondary copper and manganese ores
associated with the Boleo Formation is under ongoing
investigation. Conly and Scott (2000) believe the for-
mation of copper sulfide involved hydrothermal alter-
ation of clayey tuffs within the Boleo Formation. The
manganese oxide deposits formed separately, perhaps
in cold water (Freiberg, 1983).

Stratigraphy

Cretaceous basement rocks.—Cretaceous quartz
monzonite basement is overlain unconformably by

78 BULLETIN 371]

112° 1S'N

21° 22; 30"

\ 84IS24%

@.
12.5+0.4 Maa 9
12.340.4Ma <
10.0:+0.4 Ma - a.

6.76+0.9 Ma
27° 20'N i

@ Mexico highway |
Microfossil locality —— =
Megafossil locality

Loma del Tirabuz6n ("Corkscrew Hill")

K/Ar age locality (Sawlan and Smith, 1984)
‘%"r/ Ar age locality (Holt et al., 2000)
112° 20'N

Pro H

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 719

Miocene volcanic rocks and Miocene to Pleistocene
marine and nonmarine sediments that crop out in ar-
royos north and south of the town of Santa Rosalia.

Volcanic arc rocks, including the andesites of Sierra
Santa Lucta, Early to Middle Miocene.—Andesites,
basalt flows, tuffs, and volcanic breccias underlie the
Sierra Santa Lucia from west of the Boleo basin to
north of Mulegé. Referred to the Comondu Formation
by I. EK Wilson (1948), Beal (1948), Demant (1975),
and others, these rocks differ in lithology, origin, and
age from the type section of that unit. Sawlan and J.
G. Smith (1984) and Sawlan (1991) discussed the dif-
ferences between the 24—11 Ma Early to Middle Mio-
cene calcalkaline arc rocks near Santa Rosalia and the
non-arc, primarily volcaniclastic, Middle-Late Mio-
cene Comondu Formation described from the Sierra la
Giganta. Sawlan’s informal descriptive name, andes-

ites of Sierra Santa Lucia, is more appropriate for the
volcanic rocks near Santa Rosalia.

In places 10 Ma tholetitic lavas covered the volcanic
sequence before it was faulted, tilted, and deeply erod-
ed, and before seawater covered the area. A late Mid-
dle Miocene submarine rhyolite dome extruded near
the head of the present Arroyo del Boleo is a late
volcanic arc feature, especially significant for deter-
mining the age of the earliest marine deposits in this
part of the ancient gulf (J. T. Smith, 1991b).

Tertiary marine units of the Boleo basin: the Boleo,
Tirabuzén and Infierno Formations. Boleo Formation,
Middle—Late Miocene.—l. F. Wilson (1948) named the
oldest marine unit the Boleo Formation. He did not

specify a type section but probably based his descrip-

tion on the sequence exposed in Arroyo Purgatorio,
north of the town of Santa Rosalia in the quadrangle
of the same name. He described beds of conglomerate
that crop out at four separate stratigraphic levels, a
lowermost nonmarine facies overlain by alternating
beds of conglomerate, fossiliferous limestone, and
clayey tuff beds associated with later copper sulfide
and manganese oxide deposits, sandstone, and gyp-
sum.

Eight mantos or mineralized ore beds of copper de-
posits have been studied by many authors, including
Conly and Scott (2000), who investigated potential
metal sources for the copper-cobalt-zine deposits. The
manganese deposits are thickest in the northwestern
part of the area; Freiberg (1983) discussed their origin
and geological setting. I. RF Wilson and V. S. Rocha
(1955) mapped as much as 80 m of gypsum overlying
the marine limestone, and illustrated an enormous
twinned crystal exposed in Arroyo del Boleo (I. ER Wil-
son and V. S. Rocha, 1955: fig. 15). Careful study of
the gypsum deposits might locate intercalated marine
microfossiliferous layers as in the Fish Creek Gypsum
of the Salton Trough (Dean, 1996).

A basal coquina draped over a calcalkaline vent in
an unnamed northeast-flowing tributary to Arroyo del
Boleo probably formed as soon as the dome cooled.
K/Ar dates of 12.3 + 0.4 Ma and 12.5 + 0.4 Ma
constrain the age of the oldest marine fossils, which
are Tertiary-Caribbean species (Sawlan and J. G.
Smith, 1984; J. T. Smith, 1991b,c). Representative late
Middle or early Late Miocene mollusks include Fla-
bellipecten gatunensis (Toula), Nodipecten nodosus
(Linnaeus), Spondylus bostrychites (Guppy of Maury,

Text-figure 50.—Boleo basin, ridge between the headwaters of Canada Gloria (drainage in the background) and Arroyo del Boleo. A coquina
in the basal Boleo Formation drapes over mudflows and pelagonitic tuffs that dip off the flanks of a submarine dacite dome with a K/Ar age
of 12.3 + 0.4-12.5 + 0.4 (Sawlan and Smith, 1984). Arrow indicates the coquina facies that contains late Middle Miocene Tertiary-Caribbean
mollusks (J. T. Smith, 1991b, megafossil locality 84JS24). Photo, J. G. Smith, 1981.

Text-figure 51.—Tirabuz6n Formation, type section along Mexico | north of Santa Rosalia, Photo, T. M. Cronin, 1984.

Text-figure 52—Loma del Tirabuz6n, northwestern end of the type section of the Tirabuzon Formation, which dips to the southeast. The
lowest cliff-forming sandstone contains mollusks, echinoids, barnacles, and the largest recorded specimens of corkscrew trace fossils referred
to Gyrolithes. Spiral burrows were probably made by decapod crustaceans (E. C. Wilson, 1985).

Text-figure 53 —Gyrolithes fragment with surface ridges interpreted as scratch marks made by the organism that dug the burrow (E. C.
Wilson, 1985). Height 0.25 m (10 in), diameter 3 cm (1, in), Natural History Museum of Los Angeles County general collection, locality
LACMIP 4828. Photo, E. C. Wilson, 1979.

Text-figure 54.—Gyrolithes, the corkscrew part of a burrow, with an “associated Thalassinoides ‘turnaround’ ” at the lower end (E. C.
Wilson, 1985). Height 0.8 m (2 ft 8 in), Natural History Museum of Los Angeles County general collection, locality LACMIP 4828. Photo,
E. C. Wilson, 1979.

Text-figure 55.—Boleo basin arroyos mapped by I. F Wilson (1948) and I. RF Wilson and V. S. Rocha (1955), including the type section of
the Tirabuzon Formation of Carreno (1981). The type section, 4 km along Mexico | north of Santa Rosalia, is Instituto de Geologia Microfossil
locality 81 [= Natural History Museum of Los Angeles County locality LACMIP 4828]. Late Miocene *“’Ar/Ar sample is from the cinta
colorada horizon of the Boleo Formation, 40 m above its base (Holt ef a/., 2000, sample location E). Basal Boleo Formation megatossil
locality 84JS24 is shown in Text-figure 50.

8O BULLETIN 371

1917), the Tertiary-Caribbean oyster Hyotissa hyotis
(Linnaeus), and the muricid gastropod Murexiella
(Subpterynotus) textilis (Gabb) (J. T. Smith, 1991b,c).

The cinta colorada is a thin (O.5—2 m), coarse-
grained, reddish-purple, lithic tuff. The marker bed
was named by I. F Wilson (1948) for a widespread
horizon of mainly andesitic volcanic cinders, ash, and
lapilli. He reported it “*... everywhere above ore bed
no. 3” and a useful horizon for measuring offsets on
faults. The cinta colorada lies approximately 140 m
(the average was 80 m) upsection from the basal co-
quina. Holt et al. (1997, 2000) reported its Art?/Ar’?
age as 6.76 + 0.90 Ma (Text-fig. 55, location E). They
regarded the base of their section as 6.93—7.09 Ma and
the top of the Boleo Formation as 6.14—6.27 Ma; the
megatossils in the basal coquina are late Middle Mio-
cene, younger than the age of the underlying 12.3-Ma
dome and older than the 6.76 + 0.90 Ma marker ho-
rizon. The upper part of the Boleo Formation could be
as young as Late Miocene, but it is older than the
overlying Tirabuzon Formation, which contains Late
Miocene to middle Pliocene microtossils, sharks, and
mollusks.

Tirabuzon Formation, Late Miocene to Pliocene.—
The marine Tirabuzon Formation of Carreno (1981)
was originally named the Gloria Formation (1. EK Wil-
son, 1948) from a type section in Canada Gloria near
the boundary of the Santa Agueda and Santa Rosalia
quadrangles. The unit has a basal conglomerate that is
overlain by yellow to light brown fossiliferous sand-
stone, shale, and siltstone. Marine facies near the coast
grade laterally to nonmarine facies in the western Bo-
leo basin.

Because Wilson’s name was in prior use in eastern
Mexico, Carreno (1981) renamed it, in accordance
with the North American Stratigraphic Code (1983,
articles 7b and 7c). She designated a 185-m-thick sec-
tion exposed along Mexico | north of the turnoff to
Santa Rosalia as the hypostratotype (Text-figs. 51, 52,
55). Known as “Loma del Tirabuzon” or “Corkscrew
Hill,” the area is abundantly fossiliferous, best known
for |1—2-meter-long spiral, sand-filled burrows in the
yellowish to gray sandstone. These trace fossils are
referred to Gyrolithes, burrows most likely dug by
decapod crustaceans (E. C. Wilson, 1985). Early gulf
pectinids are common; they include Euvola keepi (Ar-
nold), Flabellipecten bései (Hanna and Hertlein), ““Ae-
quipecten” corteziana (Durham), “‘Aeguipecten” dal-
lasi (Jordan and Hertlein), Nodipecten subnodosus
(Sowerby), Leopecten bakeri (Hanna and Hertlein),
and Pseudamussium (Peplum) fasciculatum n. subsp.
Representative taxa were illustrated or listed by Qui-
roz-Barroso and Perrilliat (1989) and J. T. Smith

(1991c). The unit is loosely consolidated, and many
fossils are not in stratigraphic position; careful sam-
pling of im situ fossils could yield a more precise
chronostratigraphy.

Based on microfossils, Carreno (1982) assigned the
unit an Early—Middle Pliocene age. Later McDougall
(oral communication, 1996) identified Late Miocene
benthic foraminiters from the basal Tirabuzon For-
mation. We now estimate the age of this formation as
Late Miocene to Middle Pliocene. Neritic sediments in
the lower part of the Tirabuz6n Formation change
abruptly upsection to deeper water deposits of 200—
500 m, based on planktonic foraminifers (Carreno,
1982) and 34 species of sharks that suggest deposition
2—3 km offshore (Applegate and Espinosa-Arrubarena,
1981).

Infierno Formation, Late Pliocene.—The Boleo ba-
sin shallowed in the Late Pliocene during deposition
of the Infierno Formation, a basal sandstone and con-
glomeratic sand that I. EF Wilson (1948) probably de-
scribed from the south side of Arroyo el Infierno, west
of Santa Rosalia and mostly south of the present Mex-
ico 1, in the Santa Agueda and Punta Santa Ana quad-
rangles (Text-fig. 49). The unit lies with angular un-
conformity above the Tirabuzon Formation and grades
upward to nonmarine facies of the Santa Rosalia For-
mation. Well-exposed and accessible in Arroyo Santa
Agueda, the marine facies contains many of the same
Late Phocene mollusks as the Carmen-Marquer For-
mation, undifferentiated, in the Loreto embayment.

Santa Rosalia Formation, Pleistocene.—1. F. Wilson
(1948) did not designate a type section for the unit
that caps the mesas around Santa Rosalia. It uncon-
formably overlies the Infierno Formation and grades

from marine sandstone and conglomerate to loosely
consolidated nonmarine clastic sediments. Ortlieb
(1991) regarded the formation as late Early Pleisto-
cene, approximately 1 Ma in age.

Pleistocene marine terraces.—Orthieb (1991: fig. 7)
presented a map and detailed analyses of 11 transects
across 300 m of terraces in the Santa Rosalia and Cal-
dera La Reforma area. He used deep-sea cores and
paleoclimatic curves to interprete their ages as late
Early Pleistocene to Late Pleistocene.

Tres Virgenes volcanic rocks, Quaternary.—l. E
Wilson and V. S. Rocha (1955), Sawlan and J. G.
Smith (1984), and Sawlan (1991) described Quater-
nary calcalkaline flows, pumice, welded tuff, breccia,
and cinder cones from the area of the Tres Virgenes
volcanoes west of Santa Rosalia. Volcanic rocks from
Caldera la Reforma on the coast north of Santa Rosalia
were dated as >0.7—<1.5 Ma (Sawlan, 1991). Haus-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH $1

back er al. (2002) reported a radiometric age of 1.09
Ma from Schmidt (1975) for pyroclastic and lava
sheets surrounding the caldera.

Correlation of Boleo basin marine units.—Species
level redeterminations of the older Boleo Formation
mollusks are in progress. Preliminary results show

some taxa in common between the basal coquina of

the Boleo Formation and the unnamed conglomerates
of southwestern Isla Tiburon. Most are Tertiary Carib-
bean index species described from Trinidad to Panama.
The Tirabuzon Formation correlates with the lower
Matomi Member of the Puertecitos Formation on the
basis of the epitoniid gastropod Amaea (Scalina) ed-
wilsont DuShane and the pectinid Amusium toulae
(Brown and Pilsbry). The Infierno Formation is equiv-
alent to the Carmen-Marquer Formation, undifferenti-
ated of the Loreto embayment and unnamed marine
sediments of the Guadalupe basin to the north.

Isla San Marcos

Isla San Marcos lies 25 km to the southeast of Santa
Rosalia (Text-figs. 49, 56). Anderson (1950) visited
the island during the 1940 E.W. Scripps Cruise and
made a sketch map of the geology of the southern part
of the island, describing the oldest exposed rocks as
lava flows, volcanic breccia, and tuffs. An angular un-
conformity separates these units from sediments that
include a nonmarine basal sandstone containing wood
and leaf fragments, marine sandstone, gypsum with
thin interbeds of sandstone and shale, and overlying
conformable marine sandstone, conglomerate, and
limestone.

Anderson (1950) named the clastic sediments and
gypsum deposits the San Marcos Formation and inter-

preted its age as Early Pliocene. Redeterminations of
the megafossils, which include the Late Pliocene Gulf

of California index species Argopecten abietis (Jordan
and Hertlein), for this paper indicate a Late Pliocene
age, correlative with the upper part of the Tirabuzon
Formation and the Infierno Formation of I. F Wilson
(1948). Wilson’s formation names take precedence be-
cause they were published earlier than the San Marcos
Formation of Anderson (1950).

Concepcion Peninsula
Plate 2, Column 35
(Text-figs. 1, 2, 56, 60, Table 7, Appendices 1, 2)

Column ts modified from McFall (1968) and Mel-
dahl er al. (1997). Area is shown on the Mulege, El
Coyote, and San Nicolas quadrangles, GI2A57,
G12A67 and G12A68, respectively, scale 1:50,000;
and on the geologic map of Ledesma-Vazquez ef al.,
2004, scale 3 cm represents 2 km.

Overview

The Concepcion Peninsula is primarily composed of
volcanic and volcaniclastic rocks, with several local
areas underlain by marine sediments whose correlation
is under investigation. The area is important to the
tectonostratigraphic history of the gulf because the
volcanic units on the eastern side of the Peninsula rep-
resent vent or near-vent facies of a volcanic arc that
was active from 24 to 12 Ma (Sawlan, 1991). Marine
sediments in the northern and south-central parts of
the Peninsula are neither extensive nor continuous;
they could range in age from Late Miocene or Early
Pliocene in the north to Late Pliocene in the south,
based on microfossils (Carreno in Ledesma-Vazquez
and Johnson, 2001) and preliminary megafossil deter-
minations for this paper.

The Concepcion peninsula is 10-15 km wide, sep-
arated from the Baja California peninsula by Bahta
Concepcion, a 40 km long, 5—10 km wide embayment
(Text-fig. 60). Mehldahl er a/. (1997) and Foster er al.
(1997) studied the modern fauna, flora, sediments, and
subsidence rates in Bahta Concepcion.

Stratigraphy

Basement rocks and the Salto Formation, Creta-
ceous—Late Oligocene.—Bedrock in this area consists
of metamorphic rocks and Cretaceous granite for
which McFall (1968) reported an age of 78.4 + 2.9
Ma. These rocks are overlain on the eastern coast of
the peninsula by unnamed quartzose sandstone redbeds
that McLean (1988) considered Eocene(?) in age, pos-
sibly equivalent to cross bedded aeolian red sandstones
at San Carlos and Tembabiche to the south. McFall
(1968) named these beds the Salto Formation and re-
garded them as Late Oligocene, based on a tuff in the
upper part; it is the oldest unit in the Comondu Group
(Table 7).

Volcanic and volcaniclastic units, the ‘*Comondu
Group” of McFall (1968), Late Oligocene—Early Mio-
cene.—McFall (1968) used the name Comondu Group
for six new formations representing more than 4,000
m of Oligocene to Miocene volcanic and volcaniclastic
rocks (Mehldahl er a/., 1997). From oldest to youngest,
they are: the Salto Formation, Pelones Formation, Ri-
cason Formation, Minitas Formation, Pilares Forma-
tion, and the Hornillos Formation. Their lithologies,
Early to early Middle Miocene radiometric ages, and
type localities are summarized in Table 7, p. 82. Gab-
bro and tonalite intrusions penetrate these units as well
as the basement rocks, the tonalite having a K/Ar age
of 20.0 + 2.0 Ma (McFall, 1968).

A comparison of McFall’s Comondu Group with the
type section of the Comondu Formation of Heim

BULLETIN 371

Table 7.—Concepcion Peninsula, lithostratigraphic units (Text-fig. 60). Lowercase names indicate informal units that were not established

according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit

Author, reference

Lithologic description, type locality, age

Bahia Concepcion
Member

Calabaza Member

Cayuquitos Chert
Member

Comondu Group of
McFall (1968)

El Mono Chert Mem-
ber

Hornillas Formation

Infierno Formation

Minitas Formation

Pelones Formation

Pilares Formation

Ricason Formation

Johnson et al. (1997) named as

member of Infierno Formation.

Johnson er al. (1997) named as

member of Infierno Formation.

Johnson et al. (1997) named as

member of Infierno Formation.

Heim (1922) named as Forma-
tion; McFall (1968) raised to
Group.

Johnson et al. (1997) named as

member of Infierno Formation.

McFall (1968) named as part of
Comondu Group.

Wilson (1948). Johnson er al.
(1997) divided into four mem-
bers in the Concepcion Penin-
sula.

McFall (1968) named as part of
Comondu Group.

Member consists of fossiliterous and unfossiliferous limestones and
alluvial siltstones, one of which is a red layer containing localized
rhizoliths. Type section is in the south-central peninsula (shaded
rectangle, Text-fig. 60), along the western side of Arroyo Cayuqui-
tos on the road to San Sebastian (26°35'82" N, 111°38'34" W), San
Nicolas quadrangle. Late Pliocene.

Lowest member of the Infierno Formation in this area includes alluvial
conglomerate, sandstone, siltstone, and mudstone with in sifu oyster
beds in the area of Arroyo la Calabaza (26°33'52” N, 111°37'38" W)
between Cerro Prieto and Rancho Santa Rosalitta, west-central Con-
cepcion Peninsula, San Nicolas quadrangle. Late Pliocene.

Unit is a poorly consolidated chert breccia and red mudstone with an-
desitic pebbles: it was named for a 2-m-thick section on the west-
ern flank of Cerro Prieto (approximately 26°37'04"” N, 111°38'54"
W), San Nicolas quadrangle. Late Pliocene.

Formation originally described as a nonmarine conglomerate near San
José de Comondu in the Sierra la Giganta, but the name has been
used for a wide variety of lithologies in many parts of the Baja
California peninsula. Rocks from the Concepcion Peninsula have
both voleanic and volcaniclastic compositions and formed at or
near the vents of a volcanic are that occupied the present Gulf area
until the early Neogene. Late Oligocene (?)—Early Miocene.

Member is a dark brown to beige bedded chert and chert breccia with
limestone lenses and fossil mangrove roots. Type section is in the
south-central peninsula near a bend in Arroyo El Mono (26°35'8"
N, 111°40'10" W), El Coyote quadrangle. Late Pliocene.

Unit is a 150-m-thick coarse tuffaceous conglomerate that contains
volcanic clasts and a thin basal basalt flow. Type section in the
southeastern Concepeion Peninsula, San Nicolas quadrangle, is an
almost 90 m vertical cliff along the left bank of Arroyo San Sebas-
tian, 0.5 km southwest of its mouth. Early Miocene, 22—23 Ma.

Formation is a fossiliferous marine to nonmarine sandstone and con-
glomerate at type locality in Arroyo Infierno near Santa Rosalia, 70
km north of Concepcion Peninsula. McFall (1968) mapped isolated
outcrops in the northern and southwestern part of the peninsula. Li-
thologies of members in south-central Concepcion Peninsula in-
clude sandstone, siltstone, alluvial conglomerate, chert, chert brec-
cia, limestone, and mudstone. Late Pliocene.

Unit is a coarse tuffaceous conglomerate and sandstone with local basal

tuffs. 30-150 m thick. Type section is in the northeastern Concepcion

Peninsula in Arroyo de las Minitas, approximately 400 m south and

west of the lower part of the arroyo, Mulegé quadrangle. McFall

(1968) mapped it as part of the Comondu Group. Earliest Miocene.

»rmation includes interbedded reddish volcanic agglomerate, basalt

flows, minor tufts, rare tuffaceous sandstone, and conglomerate.

The more than 1,800-m-thick type section crops out in the west-

central peninsula, eastern side of coxcomb-like Los Pelones Ridge,

2.5 km north of Rancho Salto, El Coyote quadrangle. It is also ex-

posed on the western shore of Bahia Concepcion north of Cerro

San Pedro. Early Miocene, 20.0 + 2.0 Ma, based on an intruded

tonalite near Cerro Blanco, the highest peak on Concepcion Penin-

sula.

Unit is an aphanitic and porphyritic basalt, more than 90 m thick.
Type section is south of Punta Pilares and just north of the Gavilan
manganese mine, at the northeastern tip of Concepcion Peninsula,
Mulegé quadrangle. Late Oligocene to Early Miocene.

Formation consists of 1,700 m of basalt, breccia, tuff flows, and inter-
bedded agglomerates, tuffs, and andesites. Type section was not
fully worked out (fide McFall, 1968) but was regarded as south of
Punta Arena along the southwestern shore of Bahra Concepcion, El
Coyote quadrangle. Unit also crops out in the core of the Los Lla-
nos syncline at the southern end of the peninsula, Early Miocene,
17-22 Ma, youngest unit of McFall’s Comondu Group.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

Table 7.—Continued.

Lithostratigraphic unit Author, reference

Lithologic description, type locality, age

Salto Formation McFall (1968) named as part of

Comondu Group.

Carreno (1981) renamed Gloria
Formation of I. EF Wilson
(1948), preoccupied.

Tirabuzon Formation

Formation ts a distinctive voleaniclastic and tuffaceous 300-m-thick

red sandstone with large-scale cross beds and interbedded tuffs.
Type section in the west-central peninsula is along the mountain
front just north of the mouth of Arroyo Amolares and 3.2 km north
of Rancho Salto, El Coyote quadrangle. Late Oligocene, based on a
dated tuff of 28.1 + 0.9 Ma in the upper part (McFall, 1968) or
Eocene (?) (McLean, 1988).

rmation includes 185 m of fossiliferous marine sandstone, siltstone,
and conglomerate. Type section is at Loma del Tirabuzon (Cork-
screw Hill), 4 km north of the turn-off to Santa Rosalia, in the Bo-
leo basin. Yellow marine sandstone at Punta Paredon Amarillo at
the northern tip of the Concepcion Peninsula is probably this unit.
Late Miocene—middle Pliocene, based on microfossils and strati-
graphic position above dated volcanic rocks in the underlying Bo-
leo Formation at Santa Rosalia.

(1922) shows important differences in lithology and
age. Described from the Sierra la Giganta 50-60 km
to the southwest, the Comondu Formation at its type
area 1s primarily a fluvial, clast-supported, boulder to
cobble conglomerate, a distal facies derived from the

volcanic are in the area of the present gulf but not itself

an are rock. It is 12-14 Ma in age at San José de
Comondu.

McFall’s sequence occupies the medial line of an
are or a near-vent position along a volcanic arc. His
Ricason Formation, the youngest volcanic unit of the
Concepcion Peninsula, ranges in age from 17-22 Ma.
In view of these differences and the long-standing con-
fusion surrounding the Comondu Formation we use
McFall’s formational names rather than his overarch-
ing Comondu Group.

Tertiary marine sediments, northern Concepcion
Peninsula, Tirabuzon Formation and Infierno” For-
mation, Late Miocene—Early Pliocene.—Flat-lying
marine sediments referred by MacFall (1968) to the
Late (?) Pliocene Infierno (?) Formation of I. RF Wilson
(1948) unconformably overlie volcanic units in the
northern part of the peninsula. Outcrops include a
grayish white sandstone mapped by McFall near Ar-
royo del Agua Amargo, inland from Ensenada Santo
Domingo. An unnamed yellow marine fossiliferous
sandstone from Punta Paredon Amarillo, west of Punta
Concepcion, contains Late Miocene megafossils and
Late Miocene to Pliocene microfossils (Text-figs. 58,
59, 61). Carreno in Ledesma-Vazquez and Johnson
(2001) and Carreno in Ledesma-Vazquez ef al. (1999)
reported the same microfossil species from these units
as in the Tirabuzon Formation near Santa Rosalia.

Infierno Formation, central Concepcion Peninsula,
Pliocene.—Ledesma- Vazquez et al. (1997) and John-
son et al. (1997) mapped the sediments in the south-

central part of the peninsula in a 7 by 9 km area be-
tween Cerro Prieto and Rancho Santa Rosalitia (Text-
fig. 60). They recognize four small upper Pliocene ba-
sins underlain by the Late Pliocene Infierno Formation,
which they divide into four members that crop out
approximately 5 km east of the fishing camp of San
Sebastian (Johnson et al., 1997, fig. 1b). The units are
exposed in arroyos shown on the El Coyote and San
Nicolas quadrangles. Oldest to youngest, they are the
mainly alluvial Calabaza Member, El Mono Chert
(which includes fossil mangrove roots), Bahia Con-
cepcion Member and the Cayuquitos Chert Member.
Mollusks and echinoids reported from the Bahia
Concepcion Member correlate this unit with the Late
Pliocene Carmen-Marquer Formation, undifferentiat-
ed, in the onshore Loreto embayment, unnamed units
at Punta Chivato reported by Simian and Johnson
(1997), and the Infierno Formation in the Boleo basin.

San Nicolas basin
Plate 2, Column 36
(Text-figs. 60, Appendices |, 2)

Area is shown on the San Nicolas quadrangle,
G12A68, scale 1:50,000; and the geologic maps of Le-
desma-Vazquez (2000) and Ledesma-Vazquez ef al.
(2004), scale 3 cm represents 2 km.

Overview

The San Nicolas basin les between Concepcion
Peninsula and the northern Loreto embayment. It is
delimited by three fault zones: La Ramadita on the
northwest, Los Volcanes (trends west-northwest or
west to east), and San Antonio on the southeast. It
contains outcrops of an informally-named Late Plio-
cene marine unit, the San Nicolas formation, which
includes several members that are exposed in arroyos
that drain into the Gulf of California west of Punta

84 BULLETIN 371

T
Santa Rosalia Ho W
\ Isla San Marcos

@ Rancho
Pozo/well 27
Town/village
L npaved road

{> Mexico highway |

Text-fig. 60 |

Punta Chivato N

Punta Concepcion

on
“? \ ) 50 KM
% Se
?
3 { | Punta
& San Antonio =
Oo — =
{ yi > a >
Punta Pulpito N
—_
oe
) _ 7 io)
| ) Text-fig. 63 =ans
a / | g Cc
\. Purisima_g’San Isidro Vr na

= | Sa
(elk if | Ista Coronado Se
ss Comondu »- iLoreto 2, 96

, — [Lorety | *,
{ / Isla Carmen a

| |~ Text-fig. 62
(lg “Isla Danzante

Isla Monserrate

a
)Punta San Telmo

ons + a ot y ¢
SS Ne Pozo Se \< Text-fig. 69
S # ae \
S ray # | a «) FeMbabichi
Q Si \
yxy Villa an \ \

Insurgentes + \ a Isla

Ciudad San José

Constitucion

Ee
45'W ©» i]
on
Ree 30' W
\ ; Punta Paredon ae
lulege Amarillo om
@ “e\ Punta Pilares 9
ean SF
| ESD \e ge
\. Arroyo Minitas all
eX es
Vy \ ) \ oe
: 2 eS
aa? i
%, ~\ Mulegé quadrangle
267.49. N SE es cs 26° 45'N
p 7 cp ae A ae
Sts uc ) wit os ean Nicos
ie ; ‘ > ?, =
a aS C, quadrangle
& \ (Mes co
\ a =
E] Requeson \ lat \\ “p
e | °
\ z Cerro Prieto
AY) San ;
" . ANS i ° Sebastian
EM ) ve
| By San
aoe, ae ae aoe \ Nicolas
7 SR we

El Coyote quadrangle
26° 30'N

@ Mexico highway |

@ Rancho

Late Pliocene

San Nicolas Basin
NZ Hill/Cerro
aS 111
30° W

e Town/village

~~ Unpaved road

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 85

San Antonio, the prominent point northwest of Punta
Pulpito. The area is 18 km east of Mexico | by un-
paved road from Rancho El Rosarito.

Stratigraphy

Granodiorite basement rocks, Cretaceous.—Bed-
rock in this area consists of Cretaceous granodiorite.
A sample from Punta San Antonio was dated at 98.2—
99.0 Ma (D. Kimbrough i Ledesma-Vazquez, 2000).

Volcanic and volcaniclastic units, part of the ‘*Com-
ondu Group” of McFall (1968), Late Miocene.—Le-
desma-Vazquez (2000) mapped volcanic and volcani-
clastic rocks in fault contact with the Tertiary marine
sediments as andesite of Sierra Santa Lucia and re-
garded them as the “Comondu Group” of McFall
(1968). He also mapped the lowest unit as the Salto
Formation, which was described from the western
Concepcion Peninsula. As discussed above, we preter
lithologic terms for these units, which differ in age and
composition from the late Middle Miocene boulder
conglomerates of the Comondu Formation at its type
section.

San Nicolas formation, informal name, Pliocene.

The San Nicolas formation was proposed informally

by Ledesma-Vazquez (2000) for composite sections of

the Late Plhocene marine sequence that unconformably
overlies volcanic and volcaniclastic rocks in the San
Nicolas basin. The rocks are well exposed from Ar-
royo el Saucito on the northwest to Arroyo San An-
tonio, southwest of Punta San Antonio. The four new
members discussed by Ledesma-Vazquez (2000) are
formally named in Ledesma-Vazquez er al. (2006).
From oldest to youngest they are: toba San Antonio
(lithic tuff reported as “red beds” by the California
Academy of Sciences expedition collectors of 1921),
conglomerado Los Volcanes (conglomerate), lodolita

Arroyo Amarillo (mudstone), and El Saucito member
(a limy sandstone called the La Ballena member in an
earher paper by Ledesma-Vazquez and Johnson,
2001).

The San Antonio tuff crops out only at Punta San
Antonio. Ledesma-Vazquez (2000) correlated it with
the Mencenares complex of the northern Loreto em-
bayment, which Bigioggero et al. (1995) dated as 3.3
+ 0.5 Ma. The Los Volcanes conglomerate and the
marine Arroyo Amarillo mudstone overlie the tuff.

El Saucito is the youngest member, a highly fossil-
iferous biocalcarenite, coarse sand, and conglomerate
exposed in Arroyo el Saucito and to the east. Abundant
well-preserved Flabellipecten bései (Hanna and Hert-
lein) were described from this unit; the commonest
fossils in the arroyos are internal molds of marine mol-
lusks and echinoids that correlate the beds with the
Carmen-Marquer Formation, undifferentiated, of the
Loreto embayment. The San Nicolas basin sediments
are mostly flat-lying and show no reworking, in con-
trast to many of the deltaic facies and braided gravel
deposits near Loreto.

El Pulpito Rhyolite, Quaternary.—Flat-lying, light
to dark gray rhyolite was dated as 0.5 Ma by Cassa-
rubias-Unzueta and Gomez-Lopez (1994), who named
the unit Basalto el Pulpito. Ledesma-Vazquez (2000)
redescribed and renamed it Riolita el Pulpito for a se-
ries of lava flows that outcrop at Punta Pulpito.

Pleistocene marine terrace deposits and alluvium
cap the section (Ledesma-Vazquez, 2000). Ortlieb
(1991: fig. 10) published a detailed map of Pleistocene
shoreline deposits in the area.

Mulegeé area

Ortlieb (1991) also studied Pleistocene terrace de-
posits near the town of Mulegé. Uranium series ages

Text-figure 56.—Gulf islands and index map of important localities in southern Baja California Sur. Mina-Uhink (1957) named the southern

end of the Purisima-Iray basin for Pozo Iray #1, near Colonia Santo Domingo: he reported the Salada Formation in the subsurface at Pozo

Iray #2, at Puerto Adolfo Lopez Mateos.

Text-figure 57.—La Giganta (right, 5.794 m) and the Sierra la Giganta crest, view west from Arroyo el Leon, Loreto embayment. Photo, J.

T. Smith, 1986.

Text-figures 58, 59.—Amusiwn toulae (Brown and Pilsbry), U.S. National Museum hypotype no. 418203, from Punta Pared6n Amarillo.

58, ventral view (right valve on top): 59, right valve of specimen from unnamed yellow conglomeratic sandstone outcrops in the northern

Concepcion Peninsula. Unusually large and complete specimen measures 10.5 cm in height, 12.2 cm in length; the species was originally
described from the Gatun Formation, Panama. Photos, Bradford Ito, U. S. Geological Survey.

Text-figure 60.—Concepcion Peninsula, location map. Map modified from Johnson ef al. (1997) shows type sections of units described by

McFall (1968), Johnson er al. (1997), and Ledesma-Vazquez et al. (2004). Rectangle includes type sections of the Calabaza, Bahia Concepcién
and Cayuquitos Members of the Infierno Formation. CP, Cerro los Pelones; CV, Cerro Vinorama, elevation 720 m; EM, El Mono: ES, Rancho
el Salto; ESD, Ensenada Santo Domingo; SR, Rancho Santa Rosalitta. Regional index map is shown on Text-figure 56.

Text-figure 61.—Punta Paredon Amarillo and the unnamed Miocene yellow conglomeratic sandstones west of Punta Concepcién. J. R.

Ashby, Jr., collector. Photo, J. T. Smith, 1985.

86 BULLETIN 371

of the coral Porites californica Verrill from the Upper
Pleistocene +12-m terrace deposit were reported by
Ashby et al. (1987, 1988) as 124,000 + 5,000 and
144,000 + 7,000 years. Ashby (1984) and Ashby and
Minch (1987) presented detailed stratigraphic and pa-
leoecologic data from the area of the Mulegé estuary.

Loreto embayment
(Text-figs. 2, 56, 62, 63)
Overview

The Loreto embayment extends from approximately

30 km to 5 km north of Loreto, and from the base of

the Sierra la Giganta on the west to Isla del Carmen,
14 km (9 mi) offshore. The area is highly significant
in the history of the modern Gulf of California because
of its sequence of Miocene arc volcanic and volcani-
clastic sediments overlain by a thick wedge of Plio-
cene marine, nonmarine, and deltaic facies that was
deposited during the transition from extensional to
transtensional regimes. The onshore Loreto embay-

ment was mapped by McLean (1988) at a scale of

1:50,000, and as part of detailed sedimentary and tec-
tonic studies by Dorsey er al. (1997), Zanchi (1994),
and Bigioggero er al. (1995).

Long recognized as an important key to the geologic
history of the central Gulf of California, the offshore
Loreto embayment represented by the sediments on
Isla del Carmen needs further detailed mapping.

Isla del Carmen
Plate 2, Column 37
(Text-figs. 56, 62, Appendix 1)

Column modified from the geologic sketch map of

Anderson (1950: fig. 4).

Isla del Carmen is 28 km long by 3-8 km wide,
composed of unnamed volcanic and volcaniclastic
rocks overlain unconformably by a number of facies
of marine clastic deposits that were described by An-
derson (1950). We are unable to separate two of these
in the onshore basin, shown in Plate 2, Column 38 as
the Carmen-Marquer Formation, undifferentiated.

Stratigraphy

The old-
est rocks that crop out on northeastern Isla Carmen are
the reddish tuff breccias and lava flows that Anderson
(1950) referred to the Comondu Formation. Near Per-
ico Point he reported well-stratified reddish siltstone
and shale overlain by volcanic breccia that grades up-

Basement rocks, Oligocene or Miocene.

ward to well-bedded tuffaceous sandstone; it was, he
noted, **... the only place on the island where sedi-
ments were observed interbedded with lavas and brec-

cias.” Given the great confusion surrounding the use

11 ne Ww Puerto de la
: Lancha

Puerto Balandra
26° 00'N

-*/ Salinas QE

Alluvium

Calcareous dune
deposits

Andesite

, ol Arroyo
Bahia pee VS Blanco

Marquer Marquer Formation

Punta

) Colorada Carmen Formation

: 3 Unnamed sandstone
25° 50'N i,
d Cai te ae, Unnamed volcanic and

volcaniclastic rocks

Et
&

Microfossil locality
Punta

Baja
5 KM

Isla Danzante ——— — —— os

able

Text-figure 62.—Isla Carmen, map of the eastern or offshore Lor-

eto embayment. Modified from Anderson (1950), the map shows the
stratigraphic units of Durham (1950) and Anderson (1950). Micro-
fossil symbol is University of California, Berkeley, Museum of Pa-
leontology locality A-3502 of Natland (1950), now regarded as Late
Miocene—earliest Pliocene. Megatossils from the facies exposed
north of Arroyo Blanco correspond to those from western Arroyo el
Salto, Loreto onshore embayment. Regional index map is shown on
Text-figure 56.

of the Comondu Formation outside its type area in the
Sierra la Giganta, we label these units on Plate 2 as
unnamed volcanic and volcaniclastic rocks, pending
further field mapping.

Tertiary marine units: the Carmen and Marquer For-
mations of Anderson (1950). Carmen Formation, Pli-
Anderson (1950) named the Carmen Forma-
tion, a poorly bedded volcanic pebble and cobble con-
glomerate, marine sandstone, and limestone, from a
section on northeastern Isla Carmen, along the eastern
shore of Bahia Salinas to Punta Perico. In some places
it is in fault contact, in others gradational contact with
the underlying volcaniclastic rocks. As in the onshore
Loreto embayment, “islands” of volcanic rocks are
surrounded by conglomerate, indicating a depositional
surface of considerable relief.

Anderson (1950) and other early workers included
these rocks in the Salada Group because they believed

ocene.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 87

the Salada Formation consisted of “all Pliocene de-
posits,” but this is not appropriate. The Salada For-
mation was described from the Magdalena Plain of
western Baja California and differs from the Loreto
embayment formations in age, lithology, provenance
and fossils (p. 46).

Dorsey er al. (2000) studied a 1,100-m-thick section
of the Carmen Formation at Punta Perico. From base
to top the lithologies include a lower conglomerate that
they interpreted as a submarine debris flow, conglom-
erate, sandstone, marlstone, and a 3.5—3.1 Ma mud-
stone containing benthic foraminifers that indicate
depths of 400-500 m. These are overlain by dacite
breccia and boulder beds, stratified conglomerate, and
shallow shelf bioclastic limestone.

Pliocene ages assigned to marine sediments in the
Loreto embayment were originally based on molluscan
data from the 1940 E.W. Scripps cruise (Durham,
1950). More recent radiometric data refined the age to
middle to Late Pliocene (McLean, 1989; Dorsey er al.,
1997). Planktonic foraminifers from samples of the
Carmen Formation on Isla del Carmen were reported
by Natland (1950), reexamined by Ingle (1974) and
reinterpreted by McDougall (oral communication,
1996). Time scale revisions and new information on
the ranges of planktonic foraminifers suggest that Nat-
land’s sample A3502 (Text-fig. 62) is Late Miocene to
earliest Pliocene in age, Planktic Foraminiferal Zone
N17—N20, based on the co-occurrence of Globigeri-
noides obliquus Bolli and Globoquadrina humerosa
(Takayanagi and Saito). McDougall (oral communi-
cation, 1996) found age-diagnostic benthic foramini-
fers, including Bulimina uvigeriniformis and Lenticu-
lina cushmani = Robulus cushmani of Natland (1950),
in most samples from the Carmen Formation on Isla
del Carmen. The species is restricted to the Late Mio-
cene, Mohnian Stage of California and suggests that
the age of the Carmen Formation on Isla del Carmen
could be Late Miocene, probably Planktic Foraminit-
eral Zone N17a, upper Mohnian Stage, 8-6 Ma, based
on benthic foraminifers.

Marquer Formation, Pliocene.—The Marquer For-
mation was described by Anderson (1950) from sea-
cliffs and arroyos east of Marquer Bay in the south-
western part of Isla del Carmen. It is a white to grayish
white calcareous conglomerate containing volcanic
pebbles, sandstones, marls, coquina, algal limestone,
coral fragments, and abundant megafossils regarded by
Durham (1950) as Late Pliocene in age. Except for the
pectinids and echinoids, most of the fossils are
leached. In places the unit is unconformable or in fault
contact with underlying volcanic and volcaniclastic
rocks. Anderson (1950) also reported outcrops at

Puerto Balandra. The unit is overlain by lavas, dunes,
alluvium, beach deposits and, at Bahia Salinas, evap-
orite deposits (Kirkland er al., 1966).

A third unit described by Anderson (1950), the San
Marcos Formation, is discussed above under the Boleo
basin (p. 81). Its age is reinterpreted from megafossils
from its type section on Isla San Marcos, southeast of
Santa Rosalia, as a Late Pliocene equivalent of the
earlier named Infierno Formation of I. E Wilson
(1948). Beds near Arroyo Blanco on Isla del Carmen
yielded Argopecten abietis (Jordan and Hertlein), a
common pectinid index species in the Carmen, Mar-
quer, and Infierno Formations.

Andesite flows.—Andesite flows cap the section on
the northwestern part of the island, east of Puerto Bal-
andra and south of Oto Bay (Anderson, 1950).

Isla Monserrate
(Text-figs. 1, 56)

Reconnaissance collections of marine mollusks by
J. A. Minch in 1987 from unnamed rocks on north-
western Isla Monserrate, 30 km southwest of Isla del
Carmen, yielded a deeper water facies containing an
assemblage of the marine epitoniid gastropod Sthen-
orhytis toroense (Dall) and abundant disarticulated
specimens of Flabellipecten bései (Hanna and Hert-
lein) of probable Pliocene age. Megafossils collected
by the 1940 E.W. Scripps cruise suggest the unit on
the southeastern side of the island is the Carmen For-
mation (University of California, Berkeley, Museum
of Paleontology localities A-3568, A-3566) (Ander-
son, 1950).

Loreto basin
Plate 2, Column 38
(Text-figs. 1, 2, 56, 63-67, Appendices 1, 2)

Column modified from McLean (1988). Area is
shown on the Loreto quadrangle, GI12A88, 1:50,000;
and the geologic maps of McLean (1988, 1989), An-
derson (1950), Zanchi (1994), Bigioggero er al.
(1995), and Dorsey et al. (1997).

Overview

The onshore Loreto embayment was recognized by
workers from Gabb (1869a) to the present as a highly
significant area of good access and exposures for map-
ping and topical studies of all kinds. The marine sed-
iments that Anderson (1950) and Durham (1950) re-
ferred to the Carmen Formation and the Marquer For-
mation were classified as lithofacies associated with
different depositional environments by Dorsey et al.
(1997). Zanchi in Piazza and Robba (1994, 1998) gave
the units informal names. In this paper we regard the

88 BULLETIN 371

onshore marine sequence as Carmen-Marquer Forma-
tion, undifferentiated. Recent workers have focused on
the half-graben setting of the basin, the zone of normal
faults, and the irregular topography of underlying vol-
canic and volcaniclastic rocks on which later sedi-
ments were deposited. Arroyos exposing many differ-
ent facies are shown in a sketch map from McLean
(1989) (Text-fig. 63).

Stratigraphy

Cretaceous granitic and prebatholithic metamor-
phic basement rocks.—Cretaceous granitic batholithic
rocks and prebatholithic metasedimentary basement
rocks are exposed in the southwestern Loreto basin

between the Sierrra la Giganta and the area west of

Mexico |. They were mapped and discussed by Mc-
Lean (1988), who also reported an Eocene (?) quartz-

ose red cross-bedded sandstone in the upper part of

Arroyo de Gua and an aeolian red sandstone in Arroyo
el Salto (Text-fig. 67). Tunesi et al. (2000) analyzed
the chemistry of gabbro and pyroxenite xenoliths in
the granite, interpreting them as fragments of lower
crust brought to the surface by lavas that are less than
| Ma in age.

Unnamed volcanic and volcaniclastic rocks, Late
Oligocene—Middle Miocene.—Late Oligocene, Early
Miocene, and Middle Miocene volcaniclastic and near-
vent volcanic facies, welded tuffs, breccias, and lavas
overlie the Loreto basin basement rocks (Text-fig. 66).
Referred to the Comondu Formation by many workers,
these vent and near-vent facies of the Miocene vol-
canic are differ from that unit in age and lithology. In
part they represent source rocks for the younger fluvial
deposits of the type Comondu Formation that consti-
tutes much of the Sierra la Giganta to the west (Text-
fig. 57). McLean (1988, 1989) discussed their lithol-
ogies and distribution; he reported K/Ar and fission
track ages on zircons that range between 20.4 and 29.5
Ma for a welded tuff interbedded with the volcanic
and volcaniclastic complex. Chavez (1978) referred
these rocks to the Huertitas formation, informal name,
and the Comondu Formation.

Carmen-Marquer Formation, undifferentiated, Late
Pliocene.—The Carmen and Marquer Formations,
originally described from Isla del Carmen, have been
sampled extensively in sections exposed in Arroyo de
Arce and Arroyo de Gua, 4—6 km north of the town
of Loreto. The sandstones, conglomerates, and coqui-
nas in these outcrops represent many facies that are
mappable only at very large scales. Abundant Pliocene
mollusks are found throughout the section. McLean
documented the Late Pliocene deposition with three K/

Ar ages on water-lain tuffs within the sediments: 3.3
+ 0.5, 2.1 + 0.4, and 1.9 + 0.5 Ma (Text-fig. 65).

Umhoefer et al. (1994, 1996) divided the Pliocene
Loreto basin sediments into four informal stratigraphic
units that overlie the Miocene volcanic rocks with an-
gular unconformity. Oldest to youngest, they are: se-
quence |, nonmarine alluvial fan, conglomerate, and
sandstone; sequence 2, shallow marine fossiliferous
sandstone; sequence 3, shell-rich bioclastic limestone
with minor sandstone and conglomerate; sequence 4,
rocky shoreline facies overlain by carbonate shelf de-
posits. Tuffs from sequences 2, 3, and 4 of Umhoefer
et al. (1994) have Late Pliocene Art’/Ar* ages of 2.61
+ 0.01 Ma, 2.46 + 0.06 Ma, 2.36 + 0.02 Ma, and
1.97 + 0.02 Ma, respectively.

A few data suggest isolated, older marine facies
west of Mexico | in Arroyo Amarillo, a north-flowing
tributary to Arroyo Leon (McLean, 1988; fossil local-
ity h = J. T. Smith locality 86JS8). Most of the radio-
metric dates from the Loreto area indicate that the ma-
rine deposits range from middle Pliocene to Late Pli-
ocene (McLean, 1989; Dorsey ef al., 1997), but dia-
tomaceous beds in Arroyo Amarillo contain earliest
Pliocene foraminifers (H. Olson, oral communication,
1986) and Late Miocene—earliest Pliocene open-ocean
diatoms of the 7halassiosira oestrupti Zone Ma (Bar-
ron, oral communication, 1986, in J. T. Smith, 199 1c:
638).

Zanchi in Piazza and Robba (1994, 1998) proposed
new names for the Carmen-Marquer Formation, un-
differentiated, but they remain informal until published
with designated type sections. From oldest to youn-
gest, the lower sequence is: La Vinorama conglomer-
ate, Cerro Microondas conglomerate, Una de Gato
sandstone, Piedras Rodadas sandstone, and Arroyo de
Arce Norte sandstone. The unconformable upper se-
quence includes the San Antonio formation, Canada
de Arce Sur limestone, El Troquero volcaniclastics,
San Juan limestone, and El Atacado pyroclastic rocks.
The lower sequence of debris-flow and fan-delta de-
posits rests unconformably on Miocene volcaniclastic
rocks.

Mencenares volcanic complex, Late Pliocene—Qua-
ternary.—The Cerro Mencenares volcanic complex
occupies the northern area of the basin, 30 km north
of Loreto near the coast between San Juanico and
Boca San Bruno. Bigioggero et al. (1995) studied the
Late Pliocene to Quaternary alkalai-rich andesites and
basaltic andesites and the magmatic change they re-
cord; they also dated a tuff at 3.3 Ma. Tephra and lava
flows from Cerro Mencenares interfinger with the Pli-
ocene marine sediments of the Carmen-Marquer For-
mation, undifferentiated. Bigioggero ef al. (1995) re-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 89

ferred the marine rocks to a lower sequence of fan
delta and marine deposits and an upper sequence of
yellow siltstones containing Late Pliocene foramini-
fers.
Correlation

Megafossils correlate coarse marine deposits ex-
posed in arroyos of the Loreto basin west of Mexico
1 with younger Pliocene units elsewhere in the gulf:
the Delicias Member of the Puertecitos Formation in
the Puertecitos embayment, the Infierno Formation of
the Boleo basin, and unnamed sediments at Isla Cer-
ralvo and Isla Marta Madre. Common fossils from the
Loreto embayment were listed and illustrated by Dur-
ham (1950), J. T. Smith (199 1c), and Piazza and Robba
(1994, 1998).

Eastern Magdalena embayment
Plate 2, Columns 39, 40
(Text-figs. 2, 609, Appendices 1, 2)
Overview

The eastern side of the Baja California peninsula
from approximately 120 km south of Loreto to San
Juan de la Costa represents the eastern shoreline of the
Paleogene Magdalena embayment (Text-fig. 35, p. 54).
Eight to ten million years before seawater occupied
the ancient Gulf of California, when the Baja Califor-
nia peninsula lay against mainland Mexico, this area
of eastern Baja California was the next large embay-
ment north of the La Mira basin of Michoacan (Dur-
ham ef al., 1981; Perrilliat, 1981, 1992). A forearc
basin, it received sediments from the Sierra Madre Oc-
cidental and from a volcanic are that was active be-
tween 32 Ma and 23 Ma (McDowell and Henry,
1983).

There are few geologic maps of the area (Beal,
1948; Mina-Uhink, 1957; Hausback, 1984b), except
for the region that includes the Roca Fosforica Mexi-
cana (RoFoMex) phosphorite mines at San Juan de la
Costa and the area from San Carlos to Tembabiche
(Escandon- Valle, 1977a,b), and the thesis map of Pla-
ta-Hernandez (2002). This section of the Gulf of Cal-
ifornia and major islands are shown in Text-figure 56.

San Carlos, Punta San Telmo,
Tembabiche (or Timbabichi)
Plate 2, Column 39
(Text-figs. 2, 68-71, Appendices 1, 2)

Column modified from Durham (1950) and Grimm
(1992). Area shown on the following 1:50,000 quad-
rangles: Timbabichi, G12D31; Los Burros, G12D41;
San Pedro de la Presa, G12D51, scale 1:50,000; and
on the geologic maps of Escand6n-Valle, 1977b, scale
1:10,000; and Plata-Hernandez, 2002, scale 1:10,000.

Stratigraphy

Los Pargos formation, Jurassic—Cretaceous, and
Cretaceous granite.—Basement rocks that crop out
between Arroyo San Carlos and Tembabiche were
mapped and studied by Plata-Hernandez and Schwen-
nicke (2000) and Plata-Hernandez (2002), who rec-
ognized a new Late Jurassic—earliest Cretaceous sedi-
mentary unit, the Los Pargos formation. Escandon-
Valle (1977b) mapped these rocks as Mesozoic schists
at Punta del Estero, Punta Botella, and Punta San Tel-
mo (= Punta Prieta of some maps), and on Islas Roca
Negra, Santa Cruz, and Santa Catalina. He referred
them to the San Telmo formation, an informal name
preoccupied by a unit in western Baja California (p.
23).

The Los Pargos formation is exposed north of Ar-
royo Tembabiche in a gentle anticline that strikes east-
west (Text-figs. 69, 71). It is the first Jurassic sedi-
mentary unit described from the eastern side of the
Baja California peninsula (Plata-Hernandez, 2002; Pla-
ta-Hernandez ef al., 2003). The type section on the
southern side of Ensenada los Pargos, Timbabichi
quadrangle, includes 153 m of mudstone, sandstone,
and limestone (Plata-Hernandez er al., 2003). Its Late
Jurassic to earliest Cretaceous age is based on micro-
fossils and the similarity of associated dikes to an early
Late Cretaceous trachybasalt 7 km south of Timbabi-
chi and west of Punta Montalva. The granitic rocks at
Cerro Montalva have a K/Ar age of 97.4 + 2.5 Ma
(Plata-Hernandez, 2002: 27, fig. 13). Los Pargos for-
mation microfossils include the foraminifer Globutli-
gerina oxfordiana (Grigelis), Nannoconus sp., and
Saccocoma arachnoidea (Bronniman).

Granite exposed at the core of the anticline at Punta
Botella, 1-2 km north of Ensenada los Pargos, is con-
sidered part of the Peninsular Ranges batholith. The
Los Pargos formation is overlain unconformably by
the Salto Formation.

Red sandstones, probably the Salto Formation, ear-
ly Late Oligocene.—Large-scale red cross-bedded eo-
lian sandstones and debris-flow deposits of sandy fan-
glomerates unconformably overlie basement rocks
from Arroyo San Carlos, north of Punta San Telmo,
to south of Punta Montalva, where the unit is 60-100
m thick (Escandon-Valle, 1977b; Text-fig. 70 here-
in).The basal contact is marked by a conglomerate
containing clasts of limestone and silicified porphyry
(Plata-Hernandez, 2002). Mina-Uhink (1957) and oth-
er early workers referred these rocks to the marine
Tepetate Formation, which does not crop out on the
eastern side of the Baja California peninsula.

At Punta San Telmo the upper part of the section
contains two ash-flow tuffs, the upper of which has an

90 BULLETIN 371]

: v7 Cerro Mencenares 111°
%, a + San Juan X volcanic complex 20' W
16° 96 x... @
USN Suan i San Bruno
N
9
s
Ss
=
§
v

Microondas
Loreto
Mexico highway
e Town/village
& Microfossil locality 0
@ Megafossil locality SSS
a Dated (K/Ar) Pliocene tuff

Sac Miocene near-vent facies volcanic rock
Loreto Fault
known “—_ , approximately located
and concealed and queried -?----?-

~ concealed “+-.. ,

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 9]

early Late Oligocene age of 28.1 + 0.9 Ma (Hausback,
1984b). The sandstones and fanglomerates probably
correlate with the Salto Formation at its type area in
the Concepcion Peninsula.

El Cien Formation, Timbabichi member, Late Oli-
gocene.—Some_ authors, including Plata-Hernandez
(2002), preferred the spelling **Timbabichi” following
the usage of the 1:50,000 topographic map, while oth-
ers such as Mina-Uhink (1957) and Escand6n- Valle
(1977b) used ““Tembabiche.” Grimm (1992) called
sedimentary rocks conformably overlying the Salto
Formation the ““Timbabichi formation” but did not
publish a formal description or a type section. Earlier
workers regarded the Timbabichi member as the San
Gregorio Formation (Beal, 1948; Mina-Uhink, 1957;
Hausback, 1984b), the Monterrey Formation (Escan-
don-Valle, 1977b), the undescribed San Carlos mem-
ber or the San Hilario Member of the El Cien For-
mation, formally named from 120 km south (Apple-
gate, 1986).

The new unit is the lowest member of the El Cien
Formation in this area, correlative with the San Juan
Member to the south and west and with volcaniclastic
rocks eroded from the volcanic arc. It is 130 m thick
at the type section 500-800 m northeast of the village
of Timbabichi and dips 3°—S° west (Plata-Hernandez,
2002, fig. 33); the member has many lithologies, in-
cluding characteristic dolomite beds in the lower and
middle parts, siltstone, mudstone, phosphatic sand-
stone, phosphorite, and coquina. It crops out from
north of San Carlos to south of Punta Montalva, but
does not extend as far as San Juan de la Costa (Plata-
Hernandez, 2002, and oral communication, 2003). Ex-
cept for the distinctive dolomite facies, the new mem-
ber is lithologically very similar to the San Juan Mem-
ber of Fischer er al. (1995). All of these units were

deposited, along with the younger Cerro Colorado
Member, in the extensive eastern Magdalena embay-
ment, but the Timbabichi member is restricted to the
northeastern part.

The dolomites form concretions, bioturbated beds
and resistant ledges, some with burrows of Gyrolithes
(but the corkscrews are smaller than those in the Tir-
abuzon Formation). Formerly exposed upper surfaces
are bored by lithophagid and gastrochaenid clams (Pla-
ta-Hernandez, 2002: fig. 43B); a measured section
showing facies and details of fossiliferous horizons is
presented in appendix | of her thesis.

Other fossils in the Timbabichi member, beginning
with the oldest records, include the shallow water des-
mostylid Cornwallius sookensis Vanderhoot collected
by Durham (1950) from a massive, well-cemented
sandstone and bone bed exposed at low tide at Bahta
San Carlos (Text-fig. 68). Its type locality is 35 m strat-
igraphically below a coarse-grained conglomerate and
sandstone that contains the widespread Anadara van-
derhoofi Durham marker bed; the desmostylid’s age is
constrained by a K/Ar date of 28.1 + 0.9 Ma (Haus-
back, 1984b) from the underlying formation. The sea
cow-like marine mammal foraged in shallow water
along the Late Oligocene shoreline. Plata-Hernandez
(2002) also reported a patch of coral from the lower
part of the section near Cerro Montalva, southeast of
Punta Montalva.

Many fossils are scattered throughout the unit, but
there are no age-diagnostic microfossils, only ostra-
cods and diatom fragments. Ophiuroids, barnacles, and
the sclerosponge Diplochaetetes mexicanus Wilson are
present. High-spired, turritellid-like gastropods from
the middle of the section (Plata-Hernandez, 2002, fig.
44F) resemble taxa figured by Gidde (1992 and in Fi-
scher et al., 1995) from the Cerro Colorado Member

Text-figure 63.—Loreto onshore embayment, sketch map of major arroyos modified from McLean (1989). McLean localities 2 and 12 are
shown in Text-figures 64 and 65; ages for the Pliocene tuffs range from 1.9 + 0.5 Ma-3.3 + 0.5 Ma. Microtossil locality in Arroyo el Leon

(0.6 km or 0.4 mi from km 20.6 on Mexico 1) is from ‘‘amarillo beds” that contain earliest Pliocene shelf-edge foraminifers (H. C. Olson,
oral communication, 1986). Yellow mudstones in a tributary one kilometer to the northwest yielded earliest Pliocene open-ocean diatoms of
the Thalassiosira oestrupii Zone (U.S. Geological Survey Microfossil locality Mf7247, J. A. Barron, oral communication, 1986). Regional
index map shown on Text-figure 56.

Text-figure 64.—Arroyo de Arce, prominent cliff with cavernous weathering in calcareous sandstone and coquina of the east-dipping Carmen-
Marquer Formation, undifferentiated (locality 2 of McLean, 1989). Photo, J. T. Smith, 1986.

Text-figure 65.—Loreto embayment, view west from Mexico | at km 12 of the Carmen-Marquer Formation, undifferentiated, and interbedded
Late Pliocene tuffs (McLean, 1989). Photo, J. T. Smith, 1986.

Text-figure 66.—Arc-volcanic and voleaniclastic rocks, Oligo-Miocene vent and near-vent facies north of Loreto and south of San Bruno.
Photo, J. T. Smith, 1986.

Text-figure 67.—Unnamed Oligocene (?) red cross-bedded aeolian sandstone in Arroyo El Salto, 500 m downstream from Rancho el Salto
(locality 12 of McLean, 1989 and Text-fig. 63 herein). Hill behind and to the right is composed of overlying unconformable Pliocene marine
sediments. Photo, J. T. Smith, 1986.

92 BULLETIN 371]

’2V0 me: aS
San Carlos Punta - cae
28.1+0.9 Ma San Telmo,
Punta Prieta

Cantil Colorado

Punta Botella

Ensenada
los Pargos

A "Toyo Temh pac

ah Vic he

gue
syudad *
C onstituc 100

Arroyo Agua Pps
~~ NE Punta Malpaso— ® — Town/village
Punts ~~~ Unpaved road :
el Cobre A K/Ar age locality
Sa Nope o! Type section
eC .

Ag alt /

0 3 KM
[ a —___—_ Ss |

ral
s Punta Montalva

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 93

farther west. Coquinas are more abundant in the upper
part, and bivalves are more common than gastropods,
many of which are recrystallized. Small gastropods
(O.5—1 cm height) are found in the upper dolomite and
phosphatic conglomerate beds.

Dense blocks of silty sandstones with internal molds
of two-valved mytilids occur in the proposed new
member (Plata-Hernandez, 2002: fig. 44D) in the same
lithology and distinctive concentrations that were re-
ported by Grimm (1992) from outcrops at El Mangle
(Text-fig. 30 herein). Mytilids and Anadara vander-
hoofi Durham are common in lenses and beds in the
upper 10 m of the type section. Marine vertebrate fos-
sils include an aetiocetid whale skull, marine mammal
bones, desmostylid teeth, and Oligocene shark teeth
identified as Carcharodon angustidens (Agassiz) by
Applegate and Espinosa-Arrubarena (1996). The An-
adara_ vanderhoofi Durham bed correlates this se-
quence with the the type section of Applegate’s (1986)
San Hilario Member near E] Cien.

There are no datable volcanic facies in the Timba-
bichi member, but an overlying tuff from Arroyo Tim-
babichi (25°14.780' N, 110°58.939' W) constrains its
age to Late Oligocene. The dated sample came from
a voleaniclastic unit 10 m above the contact; it has a
“Rb/*Sr age of 25.9 + 1.0 Ma (analysis for Plata-
Hernandez by the Laboratorio Universitario de Geo-
quimica Isot6pica, UNAM). Plata-Hernandez (2002:
90, fig. SOC) suggested that the Timbibichi member
ranges from approximately 28 to 26 Ma.

Escand6n-Valle (1977b) discussed several zones of

gypsum and phosphorite beds between Arroyo San
José and Tembabiche. He identified two important
phosphorite deposits, the Capa Aguilera and Capa del
Castillo, 2-5 m below porcellanite beds in Arroyo
Montalva.

Unnamed nonmarine volcaniclastic rocks, the Com-
ondu Formation or Group of authors, Late Oligocene—

Miocene.—Plata-Hernandez (2002) and Schwennicke
and Plata-Hernandez (2003) referred a 700-750 m sec-
tion of Late Oligocene to Miocene terrestrial sediments
overlying the marine rocks south of Tembabiche to the
Comondu Formation. They recognized three packages
of volcanic and volcaniclastic facies, subunits A, B,
and C, at Cerro Las Chivas, west of Punta El Cochi
(Plata-Hernandez, 2002: fig. 47). The lowest part, sub-
unit A, consists of tuffaceous sand, conglomeratic
lenses, and tuff beds, one with a *’Rb/*°Sr age of 25.9
+ 1.0 Ma. These are overlain by subunit B, a fluvial
sand and conglomerate debris-flow deposit with inter-
bedded tuffs, and subunit C, which consists of sandy
breccias and lahars. Plata-Hernandez (2002) estimated
the overall age of subunits A—C as Late Oligocene—
Middle Miocene, representing, respectively, proximal,
medial, and distal facies of a prograding volcanic arc.
The unit 1s correlative with similar facies in the Loreto
embayment.

Marine terrace deposits and alluvium, Pleistocene—
Terrace deposits containing bivalves and

Holocene.
corals and alluvium cap the section.

San Juan de la Costa
Plate 2, Column 40
(Text-figs. 30, 33, 69, Appendices 1, 2)

Column modified from Hausback (1984a,b), Grimm
(1992), and Schwennicke (1994). Areas shown on the
following 1:50,000 quadrangles: Los Burros, G12D41;
San Pedro de la Presa, G1I2D51; Punta Coyote,
G12D61; San Juan de la Costa, G12D71; the locality
maps of Fischer ef al. (1995); and the geologic maps
of Anonymous (1924), Hausback (1984a,b), Escan-
don-Valle (1977a), and Carreno (1992b).

Stratigraphy

The Paleogene Tepetate Formation, an extensive
marine unit that underlies the El Cien Formation to the

Text-figure 68.—Cornwallius bed in the El Cien Formation exposed at low tide, northern side of Arroyo San Carlos, eastern edge of the
Late Oligocene—Early Miocene eastern Magdalena embayment. S. P. Applegate, collector. (See Text-figs. 35d,e, p. 54). Photo E. C. Wilson,

1983.

Text-figure 69.—Punta San Telmo, Tembabiche, and Punta Montalva, map of the eastern Magdalena embayment. Map modified from E. C.
Wilson (1986) and Escand6n-Valle (1977b). **Tembabiche” is also spelled “Timbabichi’; Arroyo Montalva is also known as Arroyo Monte
Alban. 1, Late Jurassic—earliest Cretaceous Los Pargos formation of Plata-Hernandaz (2002), type section (Text-fig. 71)

Text-figure 70.—Red cross-bedded sandstone referred to the early Late Oligocene Salto Formation, south of Arroyo Montalva. Photo, E. C.

Wilson, 1983.

Text-figure 71.—Los Pargos formation, Late Jurassic-earliest Cretaceous unit exposed at the core of an anticline 1.5 km northeast of Arroyo
Tembabiche (Plata-Hernandez, 2002). Earlier authors regarded these rocks as schists of the “San Telmo Formation,” an informal and preoc-

cupied name. Photo, Tobias Schwennicke, 2002.

Text-figure 72.—La Paz tuff, northern side of Arroyo el Sauzoso, south of San Juan de la Costa and Punta Los Tules. An andesitic clast
from this section has a K/Ar age of 22.7 + 1.7—23.9 + 0.7 Ma (Hausback, 1984a,b). Photo, J. T. Smith, 1995.

O4 BULLETIN 371

west, is not exposed on the eastern side of the Baja
California peninsula, Although basement rocks do not
crop out in this area, subsurface units are believed to
be the same as for San Carlos and Tembabiche.

El Cien Formation, San Juan Member, Oligo-
cene.—The oldest outcrops in this area belong to the
San Juan Member of the El Cien Formation. Regarded
as the Monterrey Formation by Mina-Uhink (1957)
and Escandon- Valle (1977a,b), the member was named
by Fischer et al. (1995), based on the work of Schwen-
nicke (1992, 1994). The composite type locality in-
cludes sections at Mesa del Tesoro, Agua Amarga, and
Mesa del Junco, in the eastern San Juan de la Costa
quadrangle, 1-10 km north of the phosphate mines at
San Juan de la Costa (Text-fig. 33, p. 52). The unit is
exposed in two limbs of a shallow syncline: the eastern
outcrops are between San Juan de la Costa and Canada
de la Luz, north of 24°28’ N, the western ones between
Cerro Colorado and Arroyo Aguajito. A Late Oligo-
cene biotite-bearing ash in the latter area was dated at
25.4 + 0.2 Ma. (Hausback, 1984a,b).

The member consists of phosphatic sandstone, silt-
stone, mudstone, conglomerate, and coquina; it in-
cludes the phosphorite-bearing beds or mantos Capas
Humboldt, Capas Humboldt supertor, Capa Cuatro,
and manto principal of Escandon-Valle (1977a), which
was the most important source of the phosphorite
mined at San Juan de la Costa. The San Juan Member
is approximately 130 m thick in its type area; it thins
to 70 m to the west near El Cien and Rancho Aguajito
de Castro (Schwennicke, 1994). Galli-Olivier (1993)
summarized 17 years of reports on the phosphorites.

The San Juan Member is characterized by nine fa-
cies, including tuffaceous mudstones, silt and sand-
stone containing phosphatic conglomerates, and pel-
letal phosphorite. Late Oligocene cetaceans are abun-
dant in the middle mudstone and siltstone of the Capas
Humboldt (Gonzalez-Barba, 1997; Gonzalez-Barba et
al., 2000). The horizon known as Capa Inferior con-
tains Anadara vanderhoofi Durham, the bivalve index
species that marks the upper part of the San Hilario
Member of Applegate (1986) at its type locality. Kim
(1987: 59) reported foraminiferal assemblages that in-
clude Globigerinita glutinata (Egger) and Globiger-
inita uvula (Ehrenberg) that correlate the section at
San Juan de la Costa with Planktonic Foraminiferal
Zone P22 (approximately 28 Ma to 24 Ma) and the
section at Arroyo San Hilario. The contact between the
San Juan Member and the overlying Cerro Colorado
Member is conformable.

Cerro Colorado Member, Miocene.—The_ Cerro
Colorado Member of Applegate (1986) is not well
known in the San Juan de la Costa area. It contains

andesitic breccia, multiple welded and unwelded, in-
terbedded ash-flow tuffs, and finer-grained clastic sed-
iments than in the underlying San Juan Member. Fi-
scher et al. (1995) recognized this member at Agua
Amarga, Tarabillas, and Canada de la Luz (Text-fig.
33, p. 52), where the unit consists of 39-44 m of clas-
tic rock grading from offshore to nearshore marine de-
positional environments (Gidde, 1992).

Andesitic breccia, ignimbrites, the La Paz Tuff and
San Juan Tuff of Hausback (1984), Early Miocene.—
Hausback (1984a) mapped andesitic breccia in discon-
tinuous outcrops in the San Juan de la Costa area be-
tween Arroyo las Animas and Arroyo el Sauzoso,
south of Punta Los Tules, Baja California Sur. Massive
pink bands of rock can be seen to the west from the
malecon in La Paz; they belong to a series of rhyolitic
ignimbrites and tuffs that overlie the El Cien Porma-
tion. Hausback (1984b) named these voluminous un-
welded ash-flows the San Juan Tuff for exposures near
the mine at San Juan de la Costa. He performed chem-
ical analyses and determined a radiometric age of 16—
18 Ma for the late Early Miocene San Juan Tuff, youn-
ger than the early Early Miocene 21.0—24 Ma La Paz
Tuff, which in this area crops out only at Arroyo el
Sauzoso (Text-figs. 72, 73 herein and Hausback,
1984b: fig. 14). The La Paz Tuff is strongly welded
on the La Paz peninsula, closer to its volcanic arc
source; it is not welded at Arroyo el Sauzoso (Haus-
back, 1984b).

Sedi-
ments overlying the tuffs were referred to the Com-
onda Formation by many authors, but the facies here

Unnamed volcaniclastic rocks, Miocene.

do not include the thick, rounded boulder, clast-sup-
ported conglomerates of the type section in the Sierra
la Giganta 100-150 km to the north. They are more
like the near-vent facies of the onshore Loreto basin.
Hausback (1984a,b) reported that interbedded rhyolite
ash-flow tuffs comprise 20% of the stratigraphic se-
quence at San Juan de la Costa, and that clasts are
angular and matrix-supported.

Correlation

Before the El Cien Formation was proposed, many
studies referred the rocks of the Magdalena embay-
ment to the San Gregorio and Isidro Formations, units
described from the Purisima-Iray basin of western Baja
California Sur. Lithologies, megafossils, and datable
volcanic units differ between the two areas, both of
which have the potential for more precise correlations
based on further mapping, associated volcanic rocks,
and fossils.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 95

QJ Isla 110° W 1097 1091
(i . Espiritu 40" W 20'W
% S J Santo 0 50 KM

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/, Microwave tower
@ Megatossil locality SoFGabo San Lucas

Text-figure 73.—San Juan de la Costa and the La Paz peninsula
to Cabo San Lucas, index map of key localities. Map was modified
from Aranda-Gomez and Pérez-Venzor (1989), Schwennicke ef al.
(1996), and Fletcher er a/. (2000). Arroyo la Muela exposes the
southernmost outcrops of the Miocene Salada Formation; Miocene
whales were excavated near La Palma, the unnamed rancho shown
north of San Pedro. K/Ar ages are 21—24 Ma for the La Paz tuff at
Arroyo el Sauzoso (Hausback, 1984a,b) and 18-20 Ma for the Proy-
idencia Rhyodacite (Hausback, 1987). EC, Rancho El Carrizal: PB,
Farallones Blancos; SJC, San Juan de la Costa: faults include CF.
El Carrizal Fault; SJE San José del Cabo Fault; LTR La Trinidad
Fault.

Isla Espiritu Santo and Isla la Partida
Plate 2, Column 41
(Text-fig. 73)

Columns after Hausback (1984b, 1987) and Aranda-
Gomez and Pérez-Venzor (1988); the area is shown on
the geologic maps of Hausback (1984a,b), Aranda-Go-
mez and Pérez-Venzor (1986, 1988), and the El Coy-
ote quadrangle, G 12 D73, scale 1:50,000.

Overview
The La Paz peninsula and islands to the north-north-
west are composed primarily of Miocene volcanic
rocks overlying Cretaceous tonalite, granodiorite,
granite, and calcareous metsediments, the La Paz
Crystalline Complex of Ortega-Gutierrez (1982). The

volcanic arc that contributed these flows, tuffs, and
breccia was northeast of the present La Paz peninsula
when the area lay against mainland Mexico. An im-
portant structural feature is the La Paz Fault, which
traverses the peninsula from southern Baja California
Sur near Todos Santos to a kilometer west of Punta
Coyote and along the eastern part of the islands (Text-
fig. 73).

Isla Espiritu Santo and Isla Partida

Cretaceous (?) basement rocks crop out in the south-
eastern part of Isla Espiritu Santo. Aranda-Gomez and
Perez-Venzor (1986) described them informally as the
Pailebot augen gneiss of granitic composition that con-
tains deformed mafic dikes. They also described and
gave informal names to a number of Miocene volcanic
and volcaniclastic units that are similar to those at Pun-
ta Coyotes and La Paz. Outcrop areas were shown by
Aranda-Gomez and Peérez-Venzor (1986: text-fig. 2).
From oldest to youngest, they are the La Bonanza rhy-
olitic ignimbrite (21.2 + 0.2 Ma), Punta Lupona vol-
canic complex, Espiritu Santo volcaniclastic conglom-
erate, El Gallo rhyodacitic ignimbrite, Isla Partida vol-
canic complex, and the Pinta Tintorera, an olivine ba-
salt dated at 16.5 + 0.3 Ma. Young alluvium overlies
the section.

The islands lie mainly to the west of the La Paz
Fault; sediments were uplifted and tilted to the west,
creating deep marine embayments along the western
side of Isla Espiritu Santo. These shallow water sub-
tropical bays support abundant marine life and provide
a natural laboratory for modern carbonate sedimenta-
tion studies (Halfar, 1997; Halfar et al., 1996, 2001;
Goodfriend er al., 2000).

La Paz Peninsula
Plate 2, Column 42
(Text-fig. 73)

Stratigraphy

Basement rocks of Aranda-Gomez and Pérez-Ven-
zor (1986), Cretaceous.—Aranda-Gomez and Pérez-
Venzor (1986) recognized and named several informal
Cretaceous components within the La Paz Crystalline
Complex of Ortega-Gutierrez (1982). The oldest rocks
are the La Buena tonalite and granodiorite, which is
intercalated with calcareous metasediments in the Si-
erra de las Cruces southeast of La Paz. The La Palmilla
gabbro and the pink, medium-grained Sierra de las
Cruces granite crop out in the same area. Younger ap-
lite and pegmatite dikes differentiated from the Sierra
de las Cruces granite cut through the La Paz Crystal-
line Complex.

06 BULLETIN 371

Aranda-Gomez and Peérez-Venzor (1986: fig. 6)
identified three younger sequences of rocks that they
termed prevoleanic, volcanosedimentary and postvol-
canic units. They regarded the names as informal and
used lower case lithologic terms (tuff, sandstone) to
denote units without formal published descriptions,
specified type sections, and contact information.

Prevolcanic rocks of Aranda-Gomez and Pérez-
Venzor (1988), Late Oligocene—Miocene.—Two sedi-
mentary units of unknown age overlie the basement
rocks: a continental, possibly aeolian, red sandstone
and a medium- to fine-grained, beige to white sand-
stone known as the Cerro del Chichonal sandstone,
informal name, that crops out southeast of La Paz.
Hausback (1984b) grouped the sandstone, pebble brec-
cia, and interbedded welded ash-flow tuff in his infor-
mal “Salinas member”; he reported a K/Ar age of 25.0
+ 0.6 Ma for the ash-flow tuff. Alumirano (1970a,b)
referred the rocks to the Comondu Formation; we use
the lithologic terms of Aranda-Gomez and Pérez-Ven-
zor (1986).

Tertiary volcanic and volcaniclastic rocks, informal
names of Aranda-Gomez and Pérez-Venzor (1988),
late Early Miocene.—Basement and sedimentary
rocks are unconformably overlain by Miocene volca-
nic rocks that include a basal heterogeneous volcanic
and volcaniclastic complex, the Balandra breccia and
conglomerate, E] Caimancito pink tuff, Las Calaveras
tuff, and El Engano conglomerate. The basal complex
is overlain by the La Paz tuff, informal name of Haus-
back (1984a,b), which is thick and welded in the La
Paz peninsula, and thin but not welded near San Juan
de la Costa. In the area between La Paz and Punta
Coyotes its K/Ar age ranges from 18.7 + 1.1 to 20.6
+ 0.2 Ma. Monolithologic basaltic breccia is common
in the northern peninsula; reworked volcaniclastic con-
glomerates and breccia dominate to the southeast.
Hausback (1984b) recognized a series of ash-flow tuffs
and breccias in the area, including the La Paz tuff and
the Corumuel tuff, with ages ranging from 19.2 + 0.5
to 22.0 + 0.4 Ma.

Providencia Rhyodacite of Hausback (1987), late
Early Miocene.—Hausback (1987) formally described
a widespread rhyodacite flow from a type section at
Rancho la Divina Providencia 15 km south-southeast
of the city of La Paz (Text-fig. 73). The Providencia
Rhyodacite, which is quarried for building stone, is
unusually extensive for a single silicic lava flow. Em-
placed when very hot, it caps flat-topped hills more
than 27 km north and south of La Paz. The youngest
volcanic unit in the area, it has a K/Ar age of 19.1 +
1.2 to 19.7 + 0.2 Ma (Hausback, 1987).

The Providencia Rhyodacite was called the upper-
most member of the Comondu Formation by Hausback
(1984a,b); we include it with the Miocene volcanic
rocks of the La Paz peninsula.

Postvolcanic rocks of Aranda-Gomez and Pérez-Ven-
cor (1988), Pliocene to Quaternary. El Coyote con-
glomerate, Palmira conglomerate, Punta Coyotes
gravels, informal names.—The post-volcanic deposits
of the La Paz peninsula are semi-consolidated Pliocene
to Quaternary sediments referred informally to the Ei
Coyote conglomerate and the unconformably overly-
ing Palmira conglomerate. Aranda-Gomez and Peérez-
Venzor (1988) described the El Coyote conglomerate
as more than 50 m thick and composed of 90-95%
volcanic clasts. They mapped the unit in the north-
eastern part of the La Paz peninsula and discussed un-
certainties about its age, Miocene to Pliocene and
Pleistocene—Holocene (?). The Palmira conglomerate
is a semi-consolidated unit that crops out along the La
Paz—Pichilingue road and seems to consist largely of
Providencia Rhyodacite clasts.

Punta Coyotes gravels include slope deposits, allu-
vium, fluvial terrace deposits, and associated marine
conglomerates that were mapped by Aranda-Gomez
and Peérez-Venzor (1984). Coral species of Pocillopora
from these deposits 2 km south of Punta Coyotes have
uranium-series ages of 140,000 + 6,000 (Szabo et al.,
1990) and 123,000—138,000 (Sirkin et al., 1990).
These dates are significant because they constrain the
most recent movement on the La Paz Fault in this area
to more than 140,000 years before the present (Szabo
et al., 1990).

Other Late Pleistocene to Holocene stratigraphy was
reported by Pedrin-Avilés ef al. (1992) for terrace de-
posits in the Balandra coastal lagoon area in the north-
western La Paz peninsula. Their C'* and uranium-se-
ries ages indicate the formation of peat deposits from
4,120 + 100 years before present.

Isla Cerralvo
(Text-figs. 1, 73, 75)

Isla Cerralvo lies off the eastern La Paz peninsula,
9 km north of Punta Arena de La Ventana and ap-
proximately 15 km east of Las Cruces. It is 240 km?
in area and consists mainly of granitic and metamor-
phic rocks (Aranda-Gomez and Pérez-Venzor, 1989).
Sawlan (1991: fig. 2) showed 25-17 Ma rhyolite ig-
nimbrites on Isla Cerralvo as age equivalents of the
Late Oligocene—Early Miocene ignimbrites in the La
Paz region.

An inlier of shallow neritic Late Pliocene marine
sediments is exposed on the western side of Isla Cer-
ralvo at ““Farallones blancos” (Text-figs. 73, 75). Ma-

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 97

rine outcrops extend for perhaps 1.5 km along the
beach north of an arroyo that meets the gulf at the site
of the old Ruffo Ranch. The sediments crop out from
the strand line to cliffs more than 40 m above the
beach. Early authors such as Hertlein (1966) incor-
rectly located the fossiliferous section at El Mostrador,
10 km to the north in an area of metamorphic rocks.

Megafossils, including Argopecten abietis (Jordan
and Hertlein), Argopecten revellei (Durham), and Leo-
pecten bakeri (Hanna and Hertlein), correlate this un-
named southeast-dipping white marine sandstone, con-
glomerate and algal limestone with sections at Caleras
Beach, Isla Marta Madre, and the Carmen-Marquer
Formation, undifferentiated, of the onshore Loreto em-
bayment. These Late Pliocene taxa are not found with
the earlier Pliocene species in the Refugio Formation
at Rancho el Refugio, in the Cabo Trough south of La
Paz.

Fossiliferous Pleistocene terrace deposits were re-
ported from the southern coast of the island (Emerson,
1960).

San José del Cabo Trough
Plate 2, Columns 43, 44
(Text-fig. 1, 2, 73, 74, Table 8)

Overview

The San José del Cabo Trough lies at the south-
eastern end of the Baja California peninsula between
the coastal towns of Buena Vista and La Ribera and
the granitic hills near the Los Cabos International Air-
port. Approximately 2,000 km? in area, the elongate
basin lies in a graben between two crystalline masses.
It is bounded by the east-dipping San José del Cabo
normal fault along the Sierra la Victoria-Sierra de la
Laguna to the west and the La Trinidad Fault along
the Sierra la Trinidad to the east. The basin is underlain
by Miocene to Quaternary marine and nonmarine sed-
iments; it lacks the associated late Neogene volcanic
rocks of the La Paz peninsula. In terms of terranes, it
lies in the Southern Gulf Extensional Province and east
of the Los Cabos Block (Fletcher ef a/., 2000, 2003).

Fossiliferous marine and terrestrial sediments record
late Middle or Late Miocene to Pliocene deposition in
the ancient gulf, the transition to nonmarine condi-
tions, and a period of Neogene uplift. Significant lith-
ologic differences exist between i situ deposits in the
northern trough east of Santiago and reworked sedi-
ments west of Mexico | at the Tropic of Cancer, 25—
30 km to the south at Rancho Algodones, and east of
Santa Anita. Narrow outcrops of 10° south- and south-
east-dipping unnamed marine rocks along the coastline
between San José del Cabo and Punta Gorda are prob-
ably a different, older unit. Faunules and formations

described from the Cabo Trough in early topical stud-
ies (Appendix 1) can now be analyzed in a broader
context related to the Tertiary-Caribbean faunal prov-
ince and the ancient Gulf of California. The rocks re-
cord complex interactions between sediment sources,
sea level changes, uplift of the Los Cabos Block, basin
subsidence, and Neogene extensional faulting. Inter-
disciplinary studies involving structural geology, sed-
imentology, and paleontology constrain timing and
provide new insights on the regional history of the
basin within its larger, complex tectonostratigraphic
setting.

Arroyo la Trinidad, Rancho El Refugio
Plate 2, Column 43
(Text-figs. 74, 77-80, Table 8, Appendices 1, 2)

Column modified from McCloy (1984), Carreno
(1992a) and Martinez-Gutiérrez and Sethi (1997).
Area is shown on the Cabo Pulmo quadrangle, F12
B35, 1:50,000; and the generalized geologic maps of
Lopez-Ramos (1973) and Martinez-Gutierrez and Se-
thi (1997).

Stratigraphy

Crystalline basement rocks, Late Cretaceous.—Ar-
anda-Gomez and Peérez-Venzor (1986) included the
Mesozoic granitic basement rocks in the La Paz Crys-
talline Complex of Ortega-Gutiérrez (1982). The San
José del Cabo Trough separates two plutonic masses
in the southern peninsula: the Sierra la Victoria and
Sierra la Laguna igneous-metamorphic complex of the
Los Cabos Block to the west and the less extensive La
Trinidad igneous complex to the east. The former is
earliest Late Cretaceous, 98.4—93.4 Ma; the La Trini-
dad complex is early Late Cretaceous, 88.2 + 5.4 Ma,
(Gastil et al., 1976). Fletcher et al. (2000, 2003) and
Kohn et al. (2003) used low-temperature thermochron-
ology to study cooling rates related to exhumation
along the San José del Cabo Fault (Text-figs. 73, 74).
They determined that rapid uplift of crystalline rocks
during the Late Miocene—Early Pliocene and lower
rates since the Late Pliocene exposed the granitoids of
the Los Cabos Block.

Unnamed volcanic rocks of Martinez-Gutiérrez and
Sethi (1997), probably Late Oligocene—Miocene.
Martinez-Gutiérrez (1994) reported felsic ash, lapilli,

and rhyolitic and dacitic lava flows that crop out over
a 30 knm® area north of the Sierra la Trinidad. Steeply
dipping to vertical, the volcanic rocks strike northeast
and overlie granitoid basement. They crop out near
Cabo Pulmo and La Ribera, but have not been radio-
metrically dated. They might be related to the 25—17.6

O8 BULLETIN 37]

109° 45' W 109° 30'W 109° W
San Bartolo 23° 45'N

1
: <9) Los Barriles

\ Buena Vista

ee
\

SB La Ribera

Punta Colorada

\ >, Punta Arena

Las Cuevas

23° 30'N
Santiago

Cabo Pulmo
I

z,
/

AXA \
: 4 anid . \
Sit = i 4—
Miraflores. ! \ 4 *( Los Frailes
NAS ae |
i
bea

ee
s
vo

>
os
3

\ ps
- f ae aN Z VOS ane?

\\ got

Santa
Anita

Sierra la Laguna

YO
gann®

San José ,
— Cabo NT is Town/village

Mexico highway
23° 00'N > Punta Pamilla Unpaved road
@ a Vv Quarry
O Prominent hill/cerro
Type sectons referred to in text
= v= Unnamed Miocene

Za re :
Cabo San Lucas - marine sandstone
S90

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 99

Table 8.—San Jose del Cabo Trough, lithostratigraphic units (Text-fig. 74). Lowercase names indicate informal units that were not established
according to the North American Stratigraphic Code (1983).

Lithostratigraphic unit Author, reference Lithologic description, type locality, age
El Chorro Formation Martinez-Gutierrez and Sethi Formation consists of flat-lying, coarse-grained sandstone, conglomer-
(1997). ate, and alluvium that form young terrace deposits. Type section ts

near Rancho Chorro, 10 km southwest of Santiago, Santiago quad-
rangle. Thickest and best preserved along the western side of the
Cabo Trough. Pleistocene to Holocene.

La Calera Formation Martinez-Gutiérrez and Sethi Unit consists of 300 m of cross-bedded terrestrial red sandstone and
(1997) = Coyote Red Beds of conglomerate eroded from the Sierra la Trinidad igneous complex
McCloy (1984). informal and now exposed in the northern (lower) part of Arroyo la Trini-
name. dad. Type section is in Canada La Calera, an eastern tributary to

Arroyo la Trinidad, 2 km downstream from where the road from
Santiago enters the arroyo, Cabo Pulmo quadrangle. Older than the
late Middle or early Late Miocene marine megafossils in the over-
lying Trinidad Formation
Los Barriles Formation Martinez-Gutierrez and Sethi Formation is a nonmarine sandstone and coarse pebble to boulder

(1997). conglomerate limited to its type area near the small coastal town of
Los Barriles, 25 km north of Buena Vista, Las Cuevas quadrangle.
Late Pliocene to Early Pleistocene.

Refugio Formation Pantoja-Alor and Carrillo-Bravo Unit is a 380-m-thick, gray-white, coarse- to medium-grained, fossilif-
(1966) mentioned name; Mar- erous, marine sandstone with limestone, shale, and anomiid-rich
tinez-Gutierrez and Sethi conglomeratic facies. Type section is southeast of Santiago near
(1997) formally described and Rancho el Refugio (23°24.1' N, 109°38.5' W), Cabo Pulmo quad-
measured, rangle. Early Pliocene.

“Santiago diatomite,” Carreno (1992a) named as infor- Unit consists of 248 m of diatomaceous sediments that crop out over

informal name mal member of Trinidad For- a limited area near Rancho el Torote, Cabo Pulmo quadrangle. Up-
mation; also = Subunit C of per bathyal, Latest Miocene to middle Pliocene (Carreno, 1992a;
McCloy (1984). Pérez-Guzman, 1985).

Trinidad Formation Pantoja-Alor and Carrillo-Bravo Formation includes estuarine to marine, gray to greenish shale, mud-
(1966) named. McCloy (1984) stone, sandstone, and diatomaceous mudstone. Type section in-
recognized four informal cludes the lower, estuarine member; it is 26 km east of Santiago in
members, Subunits A—D; Mar- Arroyo la Trinidad, downstream from Rancho la Trinidad, Cabo
tinez-Gutierrez and Sethi Pulmo quadrangle. Martinez-Gutierrez and Sethi (1997) subdivided
(1997) identified three. the units into lower, middle, and upper members; the upper mem-

ber is exposed west of Cerro Sombrerito near Rancho la Soledad,
Cabo Pulmo quadrangle. Late Middle or Late Miocene at its base
to Early or middle Pliocene.

Ma ignimbrites of the La Paz region or those in the marine fossils of the overlying Trinidad Formation.
Sierra Madre Occidental (Sawlan, 1991). Field parties have suggested the rocks may correlate

: , with the Salto Formation of the Concepcion Peninsula.
La Calera Formation, older than late Middle or P

Late Miocene.—Red terrestrial sandstone and con-

glomerate that overlie basement rocks northeast of the Trinidad Formation, late Middle or early Late Mio-
La Trinidad Fault were referred to the Comondu For- cene—Pliocene.—Pantoja-Alor and Carrillo-Bravo
mation by Pantoja-Alor and Carrillo-Bravo (1966). (1966) described the Trinidad Formation, which they
Martinez-Gutiérrez and Sethi (1997) renamed the unit regarded as Pliocene, from a type area near Rancho la
La Calera Formation and mapped exposures in and Trinidad in Arroyo la Trinidad. Martinez-Gutiérrez
near a small box canyon in Arroyo la Trinidad (Text- (1994) measured a thickness of 400 m; the unit dips
fig. 79). They inferred an age older than the Miocene 10°—30° to the southwest and crops out over the north-
a

Text-figure 74.
of formally described lithologic units, many named for nearby ranchos: 1, Los Barrilles Formation: 2, El Chorro Formation, 3, La Calera
Formation; 4, Trinidad Formation; 5, Refugio Formation. Unnamed marine sediments along the coast west of Punta Gorda dip 10° S or SE
(C. H. Beal, unpublished field sheet in Stanford University’s Branner Earth Sciences Library and Map Collections). Regional index map shown
in Text-figure 73.

San José del Cabo Trough, map showing important features, ranchos and type sections. Open circles indicate type sections

100 BULLETIN 371

ern two thirds of the Cabo Trough. It represents the
earliest seawater incursion in the basin.

The basal member, Subunit A of McCloy (1984), is
equivalent to the lower facies of Martinez-Gutierrez

and Sethi (1997); it is restricted to the eastern part of

the Cabo Trough. The lower part is an in situ estuarine
siltstone with sandstone and shale that contains Mio-
cene molluscan index species such as Anadara patri-
cla (Sowerby), Melongena (M.) sp. cf. M. patula
(Broderip and Sowerby), Turritella mimetes colinensis
Hodson, and Neritina luteofasciata (Miller) that indi-
cate near-mangrove conditions (Text-figs. 74, 80).
Martinez-Gutierrez and Sethi (1997) also reported im-

pressions of plant debris. Upsection near the head of

Arroyo la Trinidad, Subunit A grades to a coarser-
grained sandstone deposited at inner neritic depths
(Smith, 1991c), and the Tertiary-Caribbean turritellid
species changes to Turritella abrupta fredeai Hodson.
The neritic facies contains the teeth of several kinds
of sharks, including Carcharadon megalodon (Agas-
siz) and the genera Hemipristis, Carcharinus, and 1s-
urus (identifications by J. R. Ashby, Jr, in 1985, of a
collection belonging to the Enrique Fiol family of Ran-
cho la Trinidad).

Martinez-Gutierrez and Sethi (1997) mapped their
middle facies near Rancho la Soledad. Its lithology
matched McCloy’s Subunit B, described as alternating
sandstones and _ siltstones containing the planktonic
foraminifers Globorotalia lenguaensis Bolli, G. may-
ert Cushman and Ellisor, and Globigerina angustium-
bilicata (Bolli).

McCloy’s Subunit B is conformably overlain by
Subunit C, the “Santiago diatomite’ of Carreno
(1992a) that crops out in Arroyo el Torote. The diat-
omite is an upper bathyal, latest Miocene to middle
Pliocene deposit (Carreno, 1992a; Pérez-Guzman,
1985) that bears a transitional microflora indicating the
convergence of the California Current and the North
Equatorial System. Representative microfossils include
the planktonic foraminifers Globigerina pachyderma
pachyderma (Ehrenberg), G. pachyderma = incompta
Cifelli, G. quinqueloba Natland, Globigerinita uvula
uvula (Ehrenberg), and Neogloboquadrina dutertrei
blowi R6gl and Boll, and calcareous nannoplankton
Discoaster brouweri Tan Sin Hok. Lithologic and fau-
nal differences between Subunits A and C suggest an
abrupt change in depth in the Late Miocene. McCloy’s
Subunit D consists of coarser, shallower water clastic
deposits that grade laterally and vertically to the Re-
fugio Formation.

Martinez-Gutiérrez and Sethi (1997) reported good
exposures of their upper facies near Rancho la Sole-
dad, Rancho la Calabaza, and Cerro Sombrerito.
Greenish and reddish quartzose sandstones and _ silt-

stones contain the Miocene gastropod genera Cancel-
laria, Pyruclia, Cymia, Solenosteira, Strombus, and
Melongena (Rodriguez-Quintana and Segura-Vernis,
1992). Some of these taxa are also found in reworked
coarse-grained sediments near the Tropic of Cancer
west of Mexico | (Text-figs. 76, 77). The facies grades
laterally and vertically to the overlying Refugio For-
mation.

Correlation

The Trinidad Formation correlates on the basis of
Miocene megafossils with parts of the Imperial For-
mation in California, the Salada Formation north of
Todos Santos, Baja California Sur, the Ferrotepec For-
mation of the La Mira Basin, Michoacan, and Tertiary-
Caribbean units such as the Gatun Formation of Pan-
ama and the Cercado Formation of the Dominican Re-
public (Smith, 199 1c).

Ingle in Gastil er al. (1999) tabulated planktonic fo-
raminiferal species from the “Santiago diatomite” that
he identified from southwestern Isla Tiburon in Unit
Msc. They include Globigerina quinqueloba Natland,
Globigerinoides extremus Bolli and Bermudez, G. ob-
liquus Boll, and G. ruber s.). (a Orbigny ). McDougall
et al. (1999) listed the same species from the northern
Salton Trough; they assigned them to Planktonic Fo-
raminiferal Zones N17 and N18, Late Miocene—Early
Pliocene. Carreno (1992a) and Pérez-Guzman (1985)
regarded the “Santiago diatomite™ microfossils as lat-
est Miocene to middle Pliocene.

Refugio Formation, Early Pliocene.—Diverse,
poorly preserved marine fossils were collected from
Rancho el Refugio more than 50 years before Marti-
nez-Gutierrez and Sethi (1997) formally named this
unit (see Appendix 1). The 360—380-m-thick type sec-
tion near Rancho el Refugio (23°24.1' N, 109°38.5'
W) includes sandstone, limestone, and shale facies that
dip 10°—20° to the southwest and contain abundant
mollusks (Text-figs. 74, 78). Diagnostic species, in-
cluding Euvola keepi (Arnold) [= E. refugioensis
(Hertlein)] and Pecten aletes Hertlein, are interpreted
as Early Pliocene in age. The Refugio Formation spe-
cies are different from the radiometrically constrained
Late Pliocene taxa found in the Loreto embayment and
at the Islas Tres Martas, Isla Cerralvo, and Bahia Gua-
dalupe in the northern Gulf of California.

Regarded as “Salada Formation” by many workers
(Beal, 1948; Mina-Uhink, 1957; Pantoja-Alor and Car-
rillo-Bravo, 1966; McCloy, 1984), the Refugio For-
mation differs in provenance, lithology, depositional
history, and a younger age. Its megafossils are latest
Miocene or Early Pliocene ancient gulf species that are
also found in the Tirabuzon Formation of the Boleo

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 101

basin. They are not present in the western Baja Cali-
fornia embayments.

Los Barriles Formation, Late Pliocene—Early Pleis-
The Los Barriles Formation is an alluvial

tocene.
sandstone and coarse-grained conglomerate that over-
lies the Refugio Formation in the northern part of the
Cabo Trough, and conformably overlies or interfingers
with it to the south. Martinez-Gutiérrez and Sethi
(1997) reported a thickness of 1,650 m.

El Chorro Formation, Late Pleistocene—Holo-
cene.—Martinez-Gutierrez and Sethi (1997) interpret-
ed the youngest continental deposit in the Cabo Trough
as Pleistocene in age, possibly mixed with Holocene
alluvium. They measured 150 m of coarse-grained

sandstone and conglomerate along the western side of

the Cabo Trough, 3—8 m in the eastern basin. The unit
is locally faulted against the Sierra la Victoria complex
and it is unconformable above the Los Barriles For-
mation.

Rancho Algodones, Santa Anita

Southern Cabo Trough
Plate 2, Column 44
(Text-fig. 74, Appendices 1, 2)

Column data from Espinosa-Arrubarrena (1979) and
reconnaissance visits by the authors. Area shown on
San José del Cabo and Palo Escopeta quadrangles,
F12B44 and F12B45, 1:50,000.

Geographic setting and lithologic units in the
southern Cabo Trough

Although there is overlap in units between the
northern and southern parts of the Cabo Trough, sed-
iment compositions differ between the rocks in three
areas: Arroyo Trinidad and Rancho el Refugio to Cerro
Sombrerito: Rancho Algodones, 25 km to the south,
and surrounding arroyos; and the hills near Santa Anita
east of the Los Cabos International Airport. The Neo-
gene sediments are generally more reworked in the
south.

Stratigraphy
Unnamed marine sandstones near Punta Gorda,
Miocene.—Beal and others (unpublished field sheets
in the Stanford University Branner Earth Sciences Li-
brary and Map Collections) mapped a well-indurated,
sparsely fossiliferous, thin, gray, marine sandstone that

dips 10° to the south and southeast along the coast
between San José del Cabo and Punta Gorda (Text-fig.
74). They assigned this unit to the “Ysidro Forma-
tion’; it might be a deposit of the protogulf subprov-
ince of Fenby and Gastil (1991), correlative with the
oldest marine rocks at Isla Tiburon. A large Lyropec-

ten sp. collected by the Beal expedition from Zacaton,
approximately 5 km northeast of Punta Gorda, con-
firms a Miocene age, but most of the other megafossils
could not be extricated from the hard matrix. A large
Flabellipecten sp. collected by the Beal expedition
from Zacaton, approximately 5 km northeast of Punta
Gorda, confirms a Miocene age, but most of the other
megafossils could not be extracted from the hard ma-
trix.

Reworked marine sediments near Rancho Algodo-
nes and Santa Anita, Miocene and Pliocene.—A 30-
m-thick section of unnamed coarse-grained, fossilif-
erous marine and non marine sandstones in the hills
near Rancho Algodones and along Arroyo el Peyote
was measured by Martinez-Gutiérrez and Sethi (1997);
they assigned the massive, coarse-grained sandstone to
the Refugio Formation. Floods have eroded the roads
and arroyos in this area, which is approximately 9 km
northeast of Santa Anita. The sandstones and mud-
stones contain vertebrates and invertebrates, both re-
worked and live-buried, from a variety of habitats (Es-
pinosa-Arrubarrena, 1979; Espinosa-Arrubarrena and
Applegate, 1981; authors’ field observations, 1995).

Miller (1980) identified Late Pliocene terrestrial and
nonmarine vertebrates from outcrops north of Rancho
Algodones and southeast of Miraflores. In Arroyo las
Tunas he reported marine beds that grade into and in-
terfinger with brown micaceous quartz sandstones, silt-
stones, and shale with an apparent dip of 6°—7° to the
east. Fossils, of which the horse was the most abun-
dant, were mostly disarticulated lower Blancan Stage
vertebrates with western North American faunal affil-
iations. Miller (1980) listed, among others: skulls,

jaws, teeth, and bones of rabbits referred to Hypolagus

sp. cf. H. verus (Kellogg); ground squirrel skull, jaw,
and teeth described as new species Ammospermophilus

Jeffriesit Miller; minimally diagnostic fragments iden-

tified as the camelid genera cf. Camelops and cf. Hem-
iauchenia;, teeth and leg bones of a cougar-like cat,
Felis? lacustris Gazin; jaws, teeth, and other bones
from a “moderately large’? species of horse, Equus
(Dolichohippus) sp. cf. E. (D.) simplicidens (Cope);
crocodile jaw fragments and teeth of Crocodylus sp.
cf. C. moreleti (Dumeril and Bocourt); rattlesnake ver-
tebra, genus cf. Crotalus sp.; a few bones referred to
the hawk genus ? Buteo; tortoise fragments of Geo-
chelone (Hesperotestudo) sp.. and lower jaw, teeth,
tusks, and other bones of the proboscid Rhynchother-
ium sp. cf. R. falconeri Osborn. The faunule suggests
a subtropical savanna environment (Miller, 1980; Tor-
res-Roldan, 1980; ongoing investigations by Wade E.
Miller and Oscar Carranza-Castaneda). Uplift and ero-
sion of the Sierra la Victoria to the west could account

102 BULLETIN 371

Text-figure 75.—Isla Cerralvo, ““Farallones blancos,”” near the site of Ruffo’s rancho. Unnamed Late Pliocene sandstones, conglomerates,

and coquina contain abundant marine megafossils that correlate the rocks with the Carmen-Marquer Formation, undifferentiated, of the Loreto
embayment. Photo, J. T. Smith, 1983

Text-figure 76.—Junction of Tropic of Cancer (approximately 23°25’ N) and Mexico |, view west at the Sierra la Laguna. Outcrops between
the highway and the sierra consist of very coarse, reworked sediments that contain fragments of robust fossils from the Refugio and upper

Trinidad Formations, Photo, J. T. Smith, 2003

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 103

for differences in sediment composition between the
vertebrate-bearing rocks and those farther north, but
detailed mapping and sedimentological studies are
needed.

Correlation

Espinosa-Arrubarrena (1979) correlated the beds at

Rancho Algodones with the Tirabuzon Formation of

the Boleo basin on the basis of shark teeth. Molluscan

fossils from unnamed, reworked, marine sediments of
the southern Cabo Trough also include a number of

taxa in common with the late Middle to Late Miocene
section at southwestern Isla Tiburon and parts of the
Imperial Formation in the Salton Trough (Gast ef al.,
1999). They include “Aequipecten” muscosus (Wood),
Chlamys mediacostata (Hanna), Anadara thauma
(Maury) [= A. carrizoensis (Reinhart) described from
the Imperial Formation], Codakia sp. cf. C. orbicularis
(Linnaeus), Conus spurius Gmelin, Strombus obliter-
atus Hanna, and Turritella imperialis Hanna.

Islas Tres Marias, Nayarit
Plate 2, Column 45
(Text-figs. 1, 81, Appendices 1, 2)

Column modified from Carreno (1985), McCloy er
al. (1988) and Chinas-Lalo (1963).

Overview

The Tres Martas Islands are important to Gulf of

California history because of their position 100 km
offshore from Punta Mita, Nayarit, Mexico. The rocks
record part of the Late Miocene to Pleistocene history
at the mouth of the Gulf, although the 1.5-km-thick
section is considerably thinner than correlative 5- to
6-km-thick Neogene sequences in the northern Gulf (J.
T. Smith, 1989). Early interpretations of a middle Pli-
ocene ancient gulf must be modified to accomodate
evidence of seawater in the northern gulf as much as
eight million years earlier than the onset of spreading
at its mouth at 4—6 Ma (Larson, 1972: Hagstrum er
al., 1987). Of the Islas Tres Martas, Isla Marta Madre
is the largest and has the most extensive stratigraphic

Isla Maria Madre

21° Arroyo Hondo Section Caleras Beach Section

Balleto Road Section

Pleistocene Conglomerate

Sandstone
Siltstone

Diatomite
Diatomaceous Shale

("1 Tuff

Andesite

5 KM

Punta
Halcones

Pliocene

Miocene

Ge
Cabo S.Lucas

Islas Tres Marias.

Text-figure 81.—Isla Maria Madre, index map and geology mod-
ified trom Carreno (1985) and McCloy ef al. (1988).

record. Late Miocene diatoms are also reported from
Isla Maria Cleofas (Pérez-Guzman, 1985).

Stratigraphy

Basement rocks consist of Cretaceous granite and
granodiorite overlain by Tertiary (7?) andesites and rhy-
olites (McCloy et al., 1988).

Units on Isla Maria Madre were designated by in-
formal location names in discussions by Carreno
(1985) and McCloy er al. (1988), whose geologic
sketch map is included here (Text-fig. 81). A section
approximately 1,145 m_ thick, including unconformi-

Text-figure 77.—Coarse-grained conglomerates with fragments of oysters, the gastropods Oliva, Melongena, and Cancellaria (Pyruclia),
west of Mexico | at the Tropic of Cancer marker. Photo, J. T. Smith, 2003.

Text-figure 78.—Refugio Formation, type section at Rancho el Refugio with poorly preserved Early Pliocene fossils, including the abundant
pectinid Euvola refugioensis (Hertlein) [= E. keepi (Arnold)|. Photo, J. T. Smith, 1983.

Text-figure 79.
la Calera with Arroyo la Trinidad. Photo, J.T. Smith, 1985.

La Calera Formation, red cross-bedded sandstones at the entrance to a box canyon in the type area near junction of Canada

Text-figure 80.—Trinidad Formation, basal Member A, type locality in Arroyo la Trinidad. The Miocene mudstone and siltstone lower facies
contains abundant double- and single-valved Anadara patricia (Sowerby) and the tiny estero-dwelling snail Neritina luteofasciata (Miller).

Photo, J. T. Smith, 1983.

104 BULLETIN 371

ties, represents Late Miocene to Late Pliocene time,
8.2 Ma—2.5 Ma. Deposition occurred during an early
Late Miocene to Early Pliocene subsidence event fol-
lowed by the Late Pliocene uplift of a seamount that
provided shallow water habitats for organisms found
as fossils in the section at Caleras Beach.

The section includes Middle Miocene (?) nonmarine
and shallow marine sandstone overlain unconformably
by younger Miocene upper to middle bathyal diato-
mite, mudstones, and limestones that are exposed at
Arroyo Hondo (McCloy er al., 1988). An unconfor-
mity separates these sediments from Early Pliocene
middle to lower bathyal sandstones and siltstones that
crop out in Balleto Road. Another unconformity di-
vides these units from Late Pliocene to Pleistocene
limestones and siltstones that occur at Caleras Beach.
Unnamed conglomerate of Chinas-Lal6 (1963), Pleis-
tocene marine terrace deposits, and alluvium cap the
section.

Carreno (1985), and McCloy e7 al. (1988) listed mi-
crofossils, including Globorotalia tumida flexuosa
(Koch) and G. scitula scitula (Brady), that indicate up-
per to middle bathyal depths for the early Late Mio-
cene diatomite, mudstone, and limestone exposed in
Arroyo Hondo. Late Pliocene shallow neritic mollusks
are abundant in the sandstones and limestones that
crop out at Caleras Beach. They were illustrated or
cited by Smith (1991c) and E. J. Moore (1984) and
include “Aequipecten” dallasi (Jordan and Hertlein),
Argopecten abietis (Jordan and Hertlein), A. revellei
(Durham), Leopecten bakeri (Hanna and Hertlein), and
Ostrea vespertina of authors. Pliocene to Holocene
species that live in the modern gulf are Oppenheimo-
pecten vogdesi (Arnold), Undulostrea megadon (Han-
ley), and Placunanomia cumingit (Broderip).

Correlation

The rocks on Isla Marta Madre are contemporane-
ous with Late Miocene to Quaternary sediments, main-
ly untossiliferous, from DSDP site 473 and Pliocene
cores from DSDP 475 and 476 (Curray er al., 1982).
Abundant fossil mollusks at Caleras Beach represent
a faunal assemblage that lived as far north as Bahia
Guadalupe during the mid-Pliocene spreading event at
the mouth of the modern gulf (Larson, 1972; Curray
and Moore, 1984: Hagstrum ef al., 1987). The mega-
fossils provide good correlation between the southern
Gulf islands, the Loreto embayment, and basins un-

derlain by the Infierno Formation from Santa Rosalia
to Concepcion Peninsula.

Punta Mita, Nayarit
(Text-fig. 1)

Unnamed marine siltstones, Late Miocene.—Ingle
in Gastil et al. (1999) recorded early and middle Late
Miocene temperate microfossils from unnamed marine
siltstones at Punta Mita, Nayarit, north of Puerto Val-
larta, Jalisco, mainland Mexico (Text-fig. 1). The for-
aminifers indicate outer neritic depths for sediments
that overlie volcanic rocks with K/Ar ages of 10.2 Ma
and 11.1 Ma (Jensky, 1975; Gastil er al., 1978).

Ingle listed the planktonic species Globigerina an-
gustiumbilicata (Boll), Neogloboquadrina continuosa
(Blow), and Orbulina suturalis (Bronniman). Benthic
foraminifers include Bolivina californica Cushman, B.
foraminata R. E. and K. C. Stewart, B. granti Rankin,
B. hughesi Cushman, B. mulleri Kleinpell and Tipton,
Buliminella brevior Cushman, B. curta Cushman, B.
elegantissima (d’Orbigny), Cassidulina panzana
Kleinpell, Epistominella reliziana (Kleinpell), Galli-
herina uvigerinaformis (Cushman and Kleinpell), and
Hansensica multicamerata (Kleinpell).

Many of these species are common in central and
southern California in temperate faunas referred to the
provincial Mohnian benthic foraminiferal stage of
Kleinpell (1938, 1980). Ingle in Gastil et al. (1999)
noted the absence of these temperate taxa at south-
western [sla Tiburon and the tropical-subtropical en-
vironment indicated by the latest Miocene—earliest Pli-
ocene faunule he reported from Unit M8c.

CONCLUSIONS

As microfossil and megafossil paleontologists, re-
spectively, we are aware that meticulous stratigraphy
can be time-consuming, but correlations that are based
on better-defined, time-stratigraphic units provide the
best resolution for dating and synthesizing large scale
tectonic events in areas of complex geology. Models
and topical studies in the ancient gulf and Baja Cali-
fornia require the best possible time constraints and
stratigraphic correlations to test and answer the larger
questions of plate tectonic history and Tertiary Carib-
bean faunal dispersal prior to the closure of the Isth-
mus of Panama. We acknowledge that correlation is
an ongoing process, and that the columns we present
here reflect current information at the time of writing.

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 105

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Wilson, I.F., and Veytia, M.

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Winker, C.D.

1987. Neogene Stratigraphy of the Fish Creek-Vallecito Section,
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Winker, C.D., and Kidwell, S.M.

1986. Southeasterly paleocurrents in Pliocene Colorado delta-
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Winterer, J.1.

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Part 1: San Diego, California to Todos Santos,

Baja California Sur

130 BULLETIN 371
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APPENDIX I: Grant and Gale, 1931
Selected Paleontological and Radiometric References, Hanna, G. D., 1925, 1927

Hanna, M. A., 1926

Hertlein and Allison, 1959
Hertlein and Grant, 1960, 1972
Jones and Miller, 1982

San Diego, Rosarito, and Rosario embayments (San Jordan. 1926. 1936

Diego to 28° N.).—

Paleodata

Microfossils

Abbott et al., 1993a,b, 1995
Buch, 1984

Bukry and Kennedy, 1969
Deméré et al., 1984

Doyle & Bandy, 1972

Holden, 1964, 1970
Lothringer, 1984

McGee, 1967

Mickey, 1970

Miller and Abbott, 1989
Pérez-Guzman, 1985

Sliter, 1968, 1984

White, 1885

Wicander, 1970

Megafossils

Abbott er al., 1995

Allison, 1955, 1974
Almazan-Vazquez and Buitron, 1984
Aranda-Manteca and Téllez-Duarte, 1989
Arnold, 1903, 1906

Ashby, 1989c

Ashby and Minch, 1984
Cushing-Woods and Saul, 1986
Deméré, 1983, 1988

Deméré et al., 1984

Durham and Allison, 1960
Emerson, 1956

Fife ert al., 1967

Filkorn, 2003

Kennedy, G. L., 1973

Kennedy, G. L. et al., 1986, 2000

Kidwell and Gyllenhaal, 1998

Ledesma-Vazquez and Johnson,1994

Lescinsky ef al., 1991

Marincovich, 1975

Miller and Abbott, 1989

Minch, 1970

Minch er al., 1984

Moore, E.J., 1968, 1983, 1984, 1987

Perrilliat, 1968

Popenoe, 1954

Popenoe and Saul, 1987

Popenoe er al., 1960

Rowland, 1972

Saul, 1970, in Kennedy, M. P. and Moore, G. W.,
1971

Saul and Popenoe, 1992, 1993

Saul and Squires, 1997

Squires and Saul, 1997, 2001

Squires et al., 1988, 1989

Téllez-Duarte and Helenes, 2002

Valentine, 1957

Valentine and Rowland, 1969

Walsh and Deméré, 1991

Webster, 1983

Zinsmeister and Paredes-Mejia, 1988

Zullo, 1992

Vertebrates

Aranda-Manteca and Téllez-Duarte, 1989
Ashby and Minch, 1984
Barnes and Aranda-Manteca, 1997

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 131

Barradas and Stewart, 1993

Demére, 1983, 1988

Deméré ef al., 1984

Gascon-Romero and Aranda-Manteca, 1997
Kopelman, 1997

Lillegraven 1972, 1976

Minch er al., 1970

Molnar, 1974

Morris, W. J., 1970, 1973, 1974, 1981
Novacek et al., 1991

Stewart and Aranda-Manteca, 1993
Walsh and Demére, 1991

Radiometric ages

K/Ar, Ar’®*/Ar’’, Sr, Fission Track, Pb-U, *°Th?*U,

1Pb?SU

Abbott et al., 1993, 1995

Aranda et al., 1993

Barthelmy, 1974

Bushee ef al., 1963
Delgado-Argote ef al.,1995 (Ar/Ar)
Dorsey, 1991 (Fission tracks)

Fife et al., 1967

Gastil et al., 1975 (K/Ar)
Hawkins, 1970

Krummenacher et al., 1975 (K/Ar)
Luhr er al., 1995

Morris, W. J., 1981

Renne et al., 1991

Rockwell et al., 1989

Vizcaino embayment.—
Paleodata
Microfossils
Berry and Miller, 1984
Davila-Alcocer and Pessagno, 1986
Drake, 1995
Helenes, 1984
Helenes and Ingle, 1979
Helenes-Escamilla, 1980, 1984
McGee, 1967
Moreno-Ruiz and Carreno, 1994
Pérez-Guzman, 1985
Pessagno et al., 1979
Smith, D. P. et al., 1993
Whalen and Carter, 2002
Whalen and Pessagno, 1984

Megafossils

Abbott et al., 1995
Alderson and Saul, 1992
Emerson, 1980
Emerson et al., 1981

Finch et al., 1979

Gabb, 1869a,b

Hertlein, 1925, 1933
Hertlein and Emerson, 1959
Hertlein and Grant, 1960
Hertz and Hertz, 1984
Imlay, 1963

Jordan and Hertlein, 1926a,b
Kilmer, 1963, 1984

Moore, E. J., 1983, 1984, 1988
Robinson, 1979b

Smith, J. T., 1984, 1991a,c
Troughton, 1974

Whalen and Pessagno, 1984

Vertebrates

Applegate er al., 1979

Aranda-Manteca and Barnes, L. G., 1993
Barnes, L. G., 1973, 1984, 1992

Barnes, L. G. et al., 1997

Gascon-Romero and Aranda-Manteca, 1997
Kilmer, 1977, 1984

Stewart, 1997

Radiometric ages

K/Ar, Ar/Ar?’, Sr, Fission Track, Pb-U, ?°Th/?4U,
231Pbh/239U

Baldwin, 1989 (Ar/Ar)

Baldwin and Harrison, 1989, 1992
Baldwin et al., 1987 (Ar/Ar)
Barnes, D. A., 1982, 1984 (U/PB)
Busby-Spera. 1988

Gastil, 1979 (K/Ar)

Kimbrough, 1980 (K/Ar), 1982 (U-PB)
Kimbrough er al., 1987 (U-PB)
Moore, T. E., 1976

Robinson, 1975 (K/Ar)

Sedlock et al., 1991

Smith, D. P. et al., 1991 (Ar/Ar)
Suppe and Amstrong, 1972 (K/Ar)
Troughton, 1974 (K/Ar)

Western embayment, San Ignacio to Arroyo San
Raymundo.—

Paleodata

Microfossils

McLean and Barron, 1988
Sorensen, 1982

Megafossils

Hertlein, 1925
Hertlein and Jordan, 1927
Smith, J. T., 1984, 1986

132 BULLETIN 371

Squires and Demetrion, 1989, 1992. 1994a,b Kim, 1987
; ; Kim and Barron, 1986
Radiometric ages Knapp, 1974
K/Ar, Ar*’/Ar*’, Sr, Fission Track, Pb-U, °Th/?*U, Martinez-Hernandez, 1992
231 Pb/722U) Martinez-Hernandez and Ramirez-Arriaga, 1997

Hausback, 1984a,b
McLean et al., 1987
Sawlan and Smith, J. G., 1984

Megafossils

Applegate, 1986

Arnold and Clark, 1917
Purisima-Iray basin.— Fischer er al., 1989, 1995
Galli-Olivier er al., 1986

Eas Gidde in Fischer et al., 1995

Microfossils Hertlein, 1925, 1968

Carreno and Cronin, 1993 Jordan, 1924, 1936

Kim, 1987 Morris, P. A. and Smith, J. T., 1995

Kim and Barron, 1987 Perrilliat, 1996

Martinez-Hernandez and Ramirez-Arriaga, 1997 Schweitzer et al., 2002

McLean and Barron, 1988 Schwennicke, 1998

Mina-Uhink, 1957 Smith, J. T.,, 1992

Squires and Demetrion, 199]

Megafossils Wehmiller and Emerson, 1980

Arnold and Clark, 1917 Wilson, E. C., 1979

Heim, 1922

Hertlein, 1925, 1968 peeve

Hertlein and Jordan, 1927 Applegate, 1986

McLean et al., 1984, 1987 Ashby, 1987

Smith, J. T., 1984, 1986, 199 1c Barnes, L. G., 1995

Squires, 1990a.b Ferrusquta-Villafranca and Torres-Roldan, 1980

Squires and Demetrion, 1990a,b, 1991, 1992, 1993, Gonzalez-Barba, 1995a, 1997

1994a.b. 1995 Gonzalez-Barba et al., 2000, 2001, 2002
Squires and Saul, 1997 Schwennicke, 1998

Schwennicke and Gonzalez-Barba, 1995
Vertebrates
Gonzalez-Barba, 1997
Gonzalez-Barba er al., 2001

Plants

Cevallos-Ferriz, 1995, 1997
Cevallos-Ferriz and Baraja-Morales, 1991, 1993,

Radiometric ages 1994
K/Ar, Ar/Ar??, Sr, Fission Track, Pb-U, 230Th/24U, Radiometric ages
231 2357 J Ses >
eee K/Ar, Ar*°/Ar?’, Sr, Fission Track, Pb-U, ?°Th/?*U,
Hausback, 1984a,b (K/Ar) 231Ph/235U

MeLean and Hausback, 1984
McLean et al., 1985, 1987
Sawlan and Smith, J. G., 1984
Smith, J. T., 1991c

Forman et al., 1971 (Th/U, Pb/U)
Hausback, 1984a,b (K/Ar)

Omura et al., 1979 (Sr)

Wehmiller and Emerson, 1980 (Sr)

Magdalena embayment.— Todos Santos and San Pedro.—

Paleodata Paleodata
Microfossils Megafossils
Carreno, 1992b Schwennicke et al., 2000
Carreno et al., 1997, 2000 Smith, J. T., 1992
Carreno in Perrilliat, 1996
Coleman, 1979 Vertebrates

Fulwider, 1976, 1984, 1991 Ferrusquia-Villafranca and Torres-Roldan, 1981

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 133

Gonzalez-Barba, 1995b
Gonzalez-Barba et al., 2000
Schwennicke ef al., 1996

Radiometric ages

K/Ar, Ar®/Ar?’, Sr, Fission Track, Pb-U, *°Th/?*U,
231Pb/235U

Aranda-Gomez and Pérez-Venzor, 1989

Part 2: Salton Trough to Islas Tres Marias

Radiometric ages

K/Ar, Ar*/Ar®, Sr, Fission Track, Pb-U, 2°Th/?¥U,
231Pp/235U

Barnard, 1968

Buising, 1990

Damon et al., 1978
Eberly and Stanley, 1978
Johnson et al., 1983
Kerr, 1982, 1984

Mace, 1981 (K/Ar)
Matti et al., 1985 (K/Ar)

Salton Trough, Whitewater River area to Sierra :
alton Troug itewater River area to Sierra Ruissard. 1979 (RIAD)

De ae Spencer er al., 1998
Paleodata Winker, 1987
Microfossils San Felipe—Puertecitos—Bahia de los Angeles—Isla
Cotton and Vander Haar, 1979, 1980, 1981 RU OR
Dean, 1996 Paleodata
Ingle, 1974 Microfossils

McDougall er al., 1999

Miller and Dockum, 1983
Quinn and Cronin, 1984

Smith, P. B., 1960, 1970
Vazquez-Hernandez er al., 1996

Megafossils

Arnold, 1906
Bramkamp, 19355
Durham, 1950

Foster, 1979

Hanna, G. D., 1926
Kew, 1914

Kidwell, 1988

Kidwell and Gyllenhaal, 1998
Powell, 1986, 1988
Siem, 1992

Taylor, 1985

Tucker ef al., 1994
Vaughan, T. W., 1917
Van Syoc, 1992
Watkins, 1992

Wilson and Cuffey, 1998
Winterer, 1975

Zullo, 1992

Zullo and Buising, 1989

Vertebrates

Downs and White, 1967

Downs and Woodard, 1961
Metzger et al., 1973

Mitchell, 1961

Thomas and Barnes, L. G., 1993

Boehm, 1984

Hertlein, 1968

Ingle, 1974; in Gastil et al., 1999
Mandra and Mandra, 1972
Martin-Barajas et al., 1993a,b, 1997
Natland, 1950

Pérez-Guzman, 1985
Vazquez-Hernandez et al., 1996

Megafossils

Andersen, 1973

Delgado-Argote and Garcta-Abdeslem, 1999
Delgado-Argote et al., 1999

Durham, 1950

Gastil et al., 1973, 1999

Hertlein, 1968

Martin-Barajas et al., 1997

Smith, J. T., 1991Ic

Stump, 1981

Radiometric ages

K/Ar, Ar/Ar?’, Sr, Fission Track, Pb-U, °Th/?U,
231Pb/235U

Delgado-Argote et al., 1995, 1997, 1998 (K/Ar, Ar/
Ar)

Desonie, 1992

Dorsey, 1991 (Fission Track)

Gastil and Krummenacher, 1977

Gastil et al., 1999

Lewis, 1994, 1996

Martin-Barajas et al., 1995, 1997 (Ar/Ar)

Nagy et al., 1999, 2000

Neuhaus, 1988a,b

134 BULLETIN 371

Oskin and Stock, 2003

Oskin et al., 2000

Smith, J. T. et al., 1985

Sommer and Garcia-Abdeslem, 1970
Stock and Hodges, 1989

Stock et al., 1999

Boleo basin, Concepcion Peninsula, Loreto basin,
and the central Gulf islands.—

Paleodata
Microfossils
Carreno, 1981, 1982
Natland, 1950

Megafossils
Cuffey and Johnson, 1997
Durham, 1947, 1950
DuShane, 1977
Emerson, 1960
Foster et al., 1997
Hanna and Hertlein, 1927
Hertlein, 1925
Johnson and Simian, 1996
Johnson er al., 1997
Ledesma-Vazquez, 2000
Ledesma-Vazquez and Johnson, 2001
Ledesma-Vazquez et al., 1997, 2004
McLean, 1987, 1988, 1989
Moore, E. J., 1983, 1984, 1987, 1988, 1992
Piazza and Robba, 1994, 1998
Quiroz-Barroso and Perrilliat, 1989
Simian and Johnson, 1997
Smith, J. T., 1991b,c
Vokes, H. E., in McFall, 1968
Wilson, E. C., 1985

Vertebrates

Applegate, 1978
Applegate and Espinosa-Arrubarrena, 1981
Flores-J., and Barnes, L. G., 1991

Radiometric ages
K/Ar, Ar*°/Ar??, Sr, Fission Track, Pb-U, °Th/?#4U,
IP b/22°U

Bigioggero et al., 1995

Casarrubias-Unzueta and Gomez-Lopez, 1994
Dorsey et al., 1995

Holt et al., 1997, 2000 (Ar/Ar)

McFall, 1968 (K/Ar)

McLean, 1987, 1989

Sawlan, 199]

Sawlan and Smith, J. G., 1984

Smith, J. T., 1991b,c

Stone, 1994

Eastern Magdalena embayment, Punta San Telmo
and Tembabiche to San Juan de la Costa and Arroyo
el Sauzoso.—

Paleodata
Microfossils
Gidde in Fischer et al., 1995
Kim, 1987
Martinez-Hernandez, 1992
Martinez-Hernandez and Ramirez-Arriaga, 1997

Megafossils
Applegate and Wilson, 1976
Durham, 1950
Fischer er al., 1995
Galhi-Olivier et al., 1993
Wilson, E. C., 1979, 1986

Vertebrates

Cruz-Marin et al., 1995
Durham, 1950
Gonzalez-Barba et al., 2000
Vanderhoot, 1942

Radiometric ages
K/Ar, Ar/Ar*’, Sr, Fission Track, Pb-U, ?°Th/?24U,
231 Pb/235U

Grimm, 1992
Hausback, 1984a,b

La Paz peninsula.—
Radiometric ages

K/Ar, Ar*/Ar?°, Sr, Fission Track, Pb-U, 2°Th/?34U,
231Ph/235U

Aranda-Gomez and Pérez-Venzor, 1986, 1988

Frizzell and Ort in Aranda-Gomez and Pérez-Ven-
zor, 1989

Hausback, 1984a,b, 1987

Pedrin-Avilés et al., 1992

Sirkin er al., 1990

Szabo et al., 1990

Cabo Trough, Isla Cerralvo and Islas Tres Marias.—
Paleodata
Microfossils
Brunner, 1971
Carreno, 1985, 1992a
Carreno and Segura-Vernis, 1992
Carreno et al., 1980, 2000
Chinas, 1963
Hanna, G. D., 1926, 1927

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

Hanna, G. D., and Brigger, 1966
Hanna, G. D., and Grant, 1926
Ingle in Gastil et al., 1999
McCloy, 1984

McCloy er al., 1988
Pérez-Guzman, 1985
Pérez-Lopez, 2002

Megatossils
Emerson, 1960
Emerson and Hertlein, 1964
Hertlein 1925, 1934, 1966
Hertlein and Emerson, 1959
Jordan and Hertlein, 1926a
Pérez-Lopez, 2002
Rodriguez-Quintana, 1988
Rodriguez-Quintana and Segura-Vernis, 1992
Schwennicke et al., 1996
Smith, J. T., 1989, 1991¢

Vertebrates

Ashby, 1987

Espinosa-Arrubarrena, 1979
Espinosa-Arrubarrena and Applegate, 1981
Ferrusquia-Villefranca and Torres-Roldan, 1980
Fierstine et al., 2001

Miller, 1980

Torres-Roldan, 1980

Radiometric ages

K/Ar, Ar*?/Ar??, Sr, Fission Track, Pb-U, ?°Th/?4U,

231Pb/25U

Gastil et al., 1976
Hausback, 1984a,b
Sirkin et al., 1990

Appendix I:
Cited Topographic Quadrangle Maps, Southern
California, Baja California, and
Baja California Sur

California topographic quadrangles mentioned in text

Quadrangle County

Arroyo Tapiado 742’

Borrego Mountain 7%’

Cabazon 742’

Carrizo Mountain
eiragsaa ys

San Diego County
Imperial County
Riverside County

Imperial County
Imperial County
San Diego County
Riverside County
San Diego County
San Diego County

Carrizo Mountain NE 74’
Del Mar 714’

Desert Hot Springs 7%’
Encinitas 714’

Escondido 714’

15’, San Diego and Im-
perial Counties; 7.5’,

135
Harper Canyon 71’ San Diego County
Jamul Mountains 74’ San Diego County
La Jolla 7%’ San Diego County
La Mesa 74’ San Diego County
National City San Diego County
Painted Gorge 742’ Imperial County
Palm Springs 15’ Riverside County
Point Loma 7%’ San Diego County
Poway 71%’ San Diego County
Rancho Santa Fe 71’ San Diego County
Whitewater 71’ Riverside County
Mexican Quadrangles cited, scale 1:50,000
Quadrangle name

(some duplicate names in use) Number
Agua Caliente Hi 11 B25
Agua Caliente H 11 B66
Agua de Higuera Hi 12. €351
Algodon H 11,B56
Ano Nuevo G 12 A56
Arroyo del Sauz I 11 D8&4
Arroyo San José G 12 A21
Bahia Asuncion G 11 B49
Bahia de Los Angeles H 12:52
Bahia Magdalena G 12 C66
Bahia Santa Maria H 11 B67
Bahia Tortugas G 11 B27
Benito Juarez G 12 C47
Boca de San Cristobal F 12 B53
Cabo Pulmo F 12 B35
Cabo San Lucas F 12: B54
Camalu H 11 BS3
Campo Juarez H 12 C42
Cerro El Huerfanito H 11 B87
Chapala H 11 D38
Ciudad Constitucion G 12 C48
Ciudad Morelos I 11 D67
Comondu G 12 A&7
Conquista Agraria F 12 Bil
Delicias Gi12Zies7
Desierto El Vizcaino G 12 A31
El Arco H 12 C82
El Agua Escondida H 11 B75
El Aguajito H ii Bs8s
El Barril H 12 C74
El Cajete G12 D72
El Canelo G 12-C277
El Caracol G 12 A24
E] Centenario G 12 D82
E] Centinela I 11 D6o4
El] Conejo G 12 D81
El Coyote G 12 A67
El Crucero H 11 D49

136

El Doctor

El Duguayjal

El Huerfanito

El Metate

El Morro

El Oasis

El Patrocinio

El Potrero

El Progreso

El Rayo

El Rosario, B.C.

El Rosario, B.C.S.
El Rosarito

El Sargento

El Sauzal de Rodriguez
El Zacaton

Emiliano Zapata
Ensenada

Estero La Bocana
Francisco R. Serrano
Francisco Zarco
Guardianes de la Patria
Guadalupe Victoria
Guayaquil

Guerrero Negro
Gustavo Diaz Ordaz
Heroes de la Independencia
Ignacio Zaragoza
Isla La Partida

Isla Montague

Isla Santo Domingo
Islas Agrarias
Jaraguay

Jesus Garcia

José Maria Morelos y Pavon
José Saldana
Juncalito

La Bocana

La Candelaria

La Fortuna del Bajio
La Islita

La Paz

La Poderosa

La Presa

La Rivera

La Rumorosa

La Trinidad

La Ventura

La Victoria

Laguna Ojo de Liebre
Laguna San Ignacio
Las Animas

Las Bombas

Las Cuevas

BULLETIN 371

11 BL?
12 A77
11 B88
11 B86
11 Bos
11 B16
12 A54
12 A66
12 C73
11 Bl4
11 B84
12 B23

lIvc79

12 D84
11 Bll
11 B23
11 DI5
IVP Bl2
12 A51
11835
I 11 D82

I 11 D85

I 11 D76

Holl DiG
G IBIS
G 12 A22
H 11 B24
G 12 C89
G 12 D62
H 11 B27
G 12 C36
I 11 D66

H 11 D28
H 11 B 34
H 11 D79

TOEREETOM MEAT TOOCT aero

12 B25

Las Pocitas
Lazaro Cardenas

Ley Federal de Aguas Numero Uno

Ligui

Llano El Chinero
Loreto

Los Burros

Los Corrales

Los Martires Uno
Los Paredones
Los Tepetates
Matom1

Meliton Albanez
Mesa El Fyidatario
Mesa Las Lagunitas
Mesa Los Tepetates
Mesa Los Venados
Mesa Piedra Rodada
Mexicali
Miraflores

Mulege

Murua

Neji

Palo Escopeta
Paso Hondo

Plan de Ayala
Potreros

Poza Grande
Primo Tapia
Prosperidad
Puertecitos

Puerto Adolfo Lopez Mateos
Puerto Alcatraz
Puerto Canoas
Puerto Chale
Puerto Cortes
Puerto Nuevo
Puerto San Carlos
Puerto San Isidro
Punta Abreojos
Punta Baja

Punta Blanco
Punta Colonet
Punta Coyote
Punta Delgadito
Punta El Diablo
Punta Estrella
Punta Eugenia
Punta Final

Punta Las Animas
Punta Malarrimo
Punta Pequena
Punta Prieta

Punta San Carlos

m= O.4) O:.@ @ Bee ie a) a) @) md) cq) a a)

Punta Santa Ana

Punta Santo Domingo
Real del Castillo Nuevo
Rosarito

Rodolfo Sanchez Taboada
Salinas Ometepec

San Antonio

San Borja

San Esteban

San Felipe

San Francisco

San Ignacio

San Isidro

San Javier

San Jeronimo

San Joaquin

San José de La Noria
San José de La Piedra
San José de Gracia

San José de Magdalena
San José del Cabo

San Juan de La Costa
San Juan de Los Planes
San Juan de Dios

San Juanico

San Luis Gonzaga, B.C.
San Luis Gonzaga, B.C.S.
San Martin

San Nicolas

San Pedro de La Presa
San Rafael

San Raymundo

San Roque

San Simon

San Venancio

San Vicente

Santa Agueda
Santa Catarina
Santa Clara

Santa Cruz

Santa Rita

Santa Rosa

Santa Rosalia
Santiago

Santo Domingo
Sierra Campo Nuevo
Sierra Cucapa
Sierra de Colombia
Sierra Los Indios
Tecate

Tepentu

Tijuana

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

—

Bl4
11 D83

TQAMADAATTMATNMMOATAATAANMATAAVIIAIITIAA

1982
11 B48
11 D117
12 C17
11 B33
12 A35
11 D26
11 B46
11 BS5
12 C68
12 A78
12 A36
12 B34
11 B54

11 B39

Lie 75

11 D48

11 B28

11 D62

12 C49

11 C69 and
I 11-€79

MQTrODTTIOADDMAGQAZLATATAZOA

Timbabichi
Todos Santos

Vale Agua Amarga
Valle Calamajue
Valle Laguna Seca
Valle las Palmas
Valle San Rafael
Venustiano Carranza
Villa Insurgentes
Villa Morelos

Number

11
11
1]
1]
1]
1]
1]
1]
1]
11
1]
11
11
1]
1]
11
1]
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11
11
11
11
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11
11
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11
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11
11
11

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Mexican quadrangles in number order

Dol
Doe2
D63
Do4
D65
D66
D6o7
C69
D71
p72
D73
D74
D75
D76
C79
D8 1
D82
D83
D8&4
D85
D806
Bll
B12
B13
B14
B15
B16
B17
B22
B23
B24
B25
B26
B27
B32
B33
B34
B35
B36
B37

Quadrangle name

Murua

Tecate

La Rumorosa

El Centinela

Mexicali

Islas Agrarias

Ciudad Morelos
Tijuana

La Presa

Valle las Palmas

Neji

La Poderosa

Sierra Cucapa
Guadalupe Victoria
Tijuana

Primo Tapia

Francisco Zarco

San Juan de Dios
Arroyo del Sauz
Guardianes de la Patria
Plan de Ayala

El Sauzal de Rodriguez
Ensenada

Real del Castillo Nuevo
El Rayo

José Saldana

El Oasis

El Doctor

Rudolfo Sanchez Taboada
El Zacaton

Héroes de la Independencia
Agua Caliente

La Ventura

Isla Montague

Puerto San Isidro

San Vicente

Jesus Garcia

Francisco R. Serrano
Llano El Chinero
Salinas Ometepec

138

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1]
1]
11
11
11
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11
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11
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11
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11
11
11
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1]
sla
11
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11
11
11
11
11
11
11
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11
11
1]
11
1]
11
1]
11
1
1]
11
11
12
12
12
12
12
12
12
12

B43
B44
B45
B46
B47
B53
B54
B55
B56
B57
Bo4
Bo5
B66
Bo7
B74
B75
B76
B77
B84
B85
BsO
B87
B88
D14
DI5
D16
D17
D18
125
D26
D27
D28
D29
D36
D37
D38
D39
D47
D48
D49
D58
D59
D69
D79
D89
C31

C41

C42
C51

€52
E53)
Cél

C62
C63

Punta Colonet
Potreros

San Rafael

Santa Clara

San Felipe

Camalu

Santo Domingo
Santa Cruz
Algodon

Punta Estrella
Lazaro Cardenas

El Morro

Agua Caliente
Bahia Santa Maria
Venustiano Carranza
El Agua Escondida
Matomr

Puertecitos

El Rosario

El Aguayjito

El Metate

Cerro El Huerfanito
El Huerfanito
Punta Baja
Emiliano Zapata
Guayaquil

San Simon

San Luis Gonzaga
Punta San Carlos
Santa Catarina

La Bocana
Jaraguay

Punta Final

Puerto Canoas

San José De La Piedra
Chapala

Valle Calamajue
Punta Blanco
Sierra de Colombia
El Crucero

Punta El Diablo
Punta Prieta
Rosarito

José Marta Morelos y Pavon
La Islita

Valle Laguna Seca
Valle Agua Amarga
Campo Juarez
Agua De Higuera
Bahia De Los Angeles
Punta Las Animas
San Borja

Los Paredones
Valle San Rafael

BULLETIN 371

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12
12
[2
i
12
12
12
12
2
11
1]
11
1]
1]
11
1]
1]
1]
11
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12

(eval
G72
C73
C74
C81
C82
C83
C84
D31
B17
B18
B19
B27
B28
B29
B38
B39
B48
B49
All
Al2
Al3
Al4
A21
A22
A23
A24
A25
A31
A32
A33
A34
A35
A36
A41
A42
A43
A44
A46
A51
A52
A53
A54
A56
A57
A63
Ao4
A65
A66
A67
A68
A74
A75
A76

San Jeronimo

Los Tepetates

El Progreso

El Barril

San Martin

El Arco

Miraflores

Los Corrales
Timbabichi

Punta Eugenia
Punta Malarrimo
Guerrero Negro
Bahia Tortugas
Sierra Los Indios
Laguna Ojo De Liebre
Puerto Nuevo

Sierra Campo Nuevo
San Roque

Bahia Asuncion

Las Bombas

Mesa Los Venados
Prosperidad

La Trinidad

Arroyo San José
Gustavo Diaz Ordaz
San Francisco

El Caracol

Punta Santa Ana
Desierto El Vizcaino
San Esteban

Los Martires Uno
San Ignacio

Santa Agueda

Santa Rosalia

Mesa El Ejidatario
Mesa Piedra Rodada
Mesa Las Lagunitas
San Joaquin

San José de Magdalena
Estero La Bocana
Punta Abreojos
Laguna San Ignacio
El Patrocinio

Ano Nuevo

Mulegé

Punta Delgadito

San José de Gracia
Mesa Los Tepetates
El Potrero

El Coyote

San Nicolas

Punta Santo Domingo
San Juanico

Paso Hondo

I22ATT
12 A78
12 A85
12 A&86
12 A87
12 A&88
12 C16
L2G
12-C18
12:E19
12 C26
12"C27
12 C29
12 C36
12C37
12 C38
12 (C39
12 C46
12 C47
12 C48
12 C49
12 C56
121€57
12 C58
123Co9
12 C66
12 C67
12 C68
12 C69
IPM O97)
12 C78

AAAAAAAMADAADAHDAAAMAAADAAAGADAMDAANDAMAANANA

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

El Duguajal G 12°C79
Santa Rosa G 12 C89
Punta Pequena G12. D341
San Isidro G 12 D41
Comondu GA D5
Loreto G 12 Dé6él
Poza Grande G 12 D62
San Venancio Gio D771
San Javier G12. )72
Juncalito G12°D73
Las Animas G12 D81
El Canelo G 12 D82
Ligui G 12 D83
Isla Santo Domingo G 12 D84
Villa Insurgentes F 12 B11
Ley Federal De Aguas Numero Uno > B12
San José De La Noria pie Ere

—- F 12 B13
Puerto Adolfo Lopez Mateos F 12 B14
Benito Juarez F 12 B2?
Ciudad Constitucion F 1 B23
Tepentu i RE
Puerto San Carlos F 12 B24
Delicias F 12 B25
Villa Morelos F 12 B33
San Luis Gonzaga F 12 B34
Bahia Magdalena F 12 B35
Puerto Alcatraz F 12 B43
Santa Rita F 12 B44
La Fortuna Del Bajfo F 12 B45
Puerto Cortes F 12 B53
Puerto Chale F 12 B54

INDEX

Las Pocitas

Ignacio Zaragoza
Timbabichi

Los Burros

San Pedro De La Presa
Punta Coyote

Isla La Partida

San Juan De La Costa
El Cajete

El Coyote

El Conejo

El Centenario

La Paz

El Sargento

Conquista Agraria

La Victoria

San Antonio

San Juan De Los Planes
Meliton Albanez

El Rosario

Las Cuevas

La Rivera

Todos Santos

Santiago

Cabo Pulmo

La Candelaria

San José Del Cabo
Palo Escopeta

Boca De San Cristobal
Cabo San Lucas

Informal stratigraphic names are given in lower case with the embayments where they are found; formal stratigraphic units are capitalized,

GDLESMSPNENOMUINUS lancaster s mS evans, Gees Batkliva Gr Sassou) 6 as 59, 61 Amaea (Scalina) @dwilsont soi. 9 aja a re ace ee 8 72, 81
abietis, Argopecten ......-......05005 74, 77, 81, 87, 97, 104 ATHIGNTIS: SPs shel a ta 3idege oh enereete. Hukgns 1 duetetane wl attehe od eh thiens 38
ADTUPIA JrEdeal. TUTTILELIA Gace. Sia 5 oo sites os Be caw 56, 100 Ammospermopnhilus JEGTIEST 5024 o.0 6 See tsa Sn He ets wee 100
ACANININGHEMEFSONE se cies dc ode ie ee we a Pe ee Ege a ee 24 Amphistegina GiDbOSG. 32025 1 J23 Gees ae te Gua Gs he ah 59, 61, 76
Acarinina pentacamerata Zone ..... 0.5.0.0 .0 02500005 50 APHUSIUIW SD: sesh. eae ens em wasy.es tcsianensas ® suena dsl eile ere Wiernte 47
advena, Pseudophragming «ii. 62. cee cee ewes ences 41, 50 Amusium 10uldé <2 6c aw he oe ee ee eee 72, 81, 84, 85
TTACQUIDECLEN ssi cies a ieee neers O 42, 66, 74, 80, 103, 104 AMUSSIOPECLEN SP. i iwscaa doen s vowes eta Ste eas Oe 35, 47

GCOMCLIS erevat ohsvz neste hahaa eran ieht seats Gast a itera sy Hier enst Nees ak 42 Amussiopectén: Va€nvlecki «0... 00.2 tics ns te ea ee ee ee 8 35

COMEZIGNG hice fuad owned se esis CRIS oo4 iss s&s 74, 80 ANAT ois FRR as oa Ss eh Ae Oye ee 1, 52, 91, 93, 100, 103

GQUASU s..0 leat ha Ros eee obs ae Nae ae olsen 80, 104 CATIZOENSIS, «ihe ties Shel ayer bial cyan @ SA aye are ane etetetel os 103

TS COSUS Ie tego Fe ete Sy iahs 2 ds SMM ee ae al Soares, oY 76, 103 DUT ICI’ 2.0. tee ae go tole Paes: Rais Se gs al maa drieods & Ee 100, 102, 103

DIUTINOMINIS’. © Pic. aie oo HEE Ge Owe Ge Hs ag Wee eee 66 PROUINA saiicipocier canisters tg scm one dees eriemtua ust sain ane, Ghee eee ees 103
Aequipecten discus a2 2 25b5e Lake aR Sa ewes oman Bil VANdETHOOfi saw dain si wee ns F bee oe 51-53, 91, 93, 94
AguarBlancavRault) (0.2 sca Gans a ein eevee sucess Sus an 225 ZO DO andersont,. TUrTitella’ o.9% wis ss % Heed eS a tana 36, 38
AouaiCalientar hauls. sates eieetetees omen evevere) hee tyersateuerets 18 andesites: of Sierra Santa Lucia™ «.......2 104, 4 als «ers als 79, 85
Alisitos; Formation’ «s.%¢ 00005 200309408 002.524 22-24, 26 angustidens, CarGRArodOn vies soi wea nee we eRe we oe eee 93
AlmejasiFormationt « ...0) sofas ates 2 o.5 2 18, 24, 28, 30-32, 35 angustiumbilicata, Globigerind .. 0.0... 0.020 50055 100, 104
AIG! SAPRATCLG’) ln hat eilers caNio te Bes sneRAa OMG! @ OE SA. le Bes wwe ee 16 ANOMIG SUDCOSIGIA sie a5 sie 5 Ga) Ge ae eas & Wie Was Goon. sce We ele 68
Alverson Formation 226 ee cee Se ot GS 62, 64, 66 Anza Formation! soc. 0.4-5 vated’ sees co oy hee ae 62, 64-66
Amado Nuevo Member, Rosarito Beach Formation .... . 19, 20 ATAChNOIdEG; SAGCCOME > o/s. 5 6 a)0 sia a es ara enahe BAS he Be 89

140 BULLETIN 371

AP CRIECLONICE MODIS oii 6 wine a4 © vieidne cht tie Besos Wales See 56
Ardath:Shale: ficsclesayaes c s-oG.a poles sre cue ape es sine neue 14, 16
Argopectencvcizs 6 6.02 siaies 31, 68, 74, 76, 77, 81, 87, 97, 104

CLD LOTES) peenemen ay ages ek = se casein wen. J4,°77,-81, 87, 97; 104

GEMUUP EUS 60a ne es es Shien Sofas anata Rianteasy 6 ene cere 76

AES GT LU vera erated a feveuaar atic e keurs avievie yeneuebeey aae yerts even iar atr sn ayia es 68, 74

percarus sethantes ere aie gitchape neta Siaheya cyese ite: he satan 31

FOVELLGI mana ccnstewrye rs ets hae os ccups en ee ures gua ene 74, 97, 104
Arroyo Amarillo Mudstone .........-------+0+eeee ees 85
Asroyo ‘Choyal, Isla‘Gedros. . 562.5 .ne sss te eee 28-30, 33
Arroyo Colorado, Magdalena embayment .... 2... 6... 50, 51
Arroyo de Arce Norte sandstone, informal name, Loreto embayment
oe cients RG Busey Aaa Lake ties iykaa Metmietaaneer ty areal ape Wwe S! Res tee oe 88
Arroyo el Salto, Loreto embayment .............. 86, 90, 91
Arroyo la Muela, southwestern Baja California Sur... 2.2...

gages oe ae eueh eae gy ee ea rae cere sues 46, 47, 49, 55-56, 95
Arroyo la Purisima, Purisima-Iray basin... 2.6.2... 36, 39-43
Arroyo la Salada, Magdalena embayment ........ 9, 46-48, 51
Arroyo la Trinidad, San José del Cabo Trough ........ 97-100
Arroyo Matomi, Puertecitos embayment ............ 9, 70, 72
Arroyo Mezquital, Purisima-Iray basin ........ 36, 37, 40-42
Arroyo Patrocinio, western embayment... .. 2.0.2... 36-39, 43
Arroyo San Carlos, eastern Magdalena embayment .......-.

Ae seseh chee cante Massie ty s8,t,cue aN Tye ets 2 Rem 10, 44, 46, 51, 89, 92, 93
Arroyo San Gregorio, Purisima-Iray basin... .......-- 42, 43
Arroyo San Hilario, Magdalena embayment .. 46, 51-53, 55, 94
Arroyo San Ignacio, western embayment ...........-+-- 36
Aroyo San Martin, Purisima-Iray basin... . 22... 0... 39-41, 43
Arroyo San Raymundo, western embayment .. 36, 37, 39, 40, 42
ashburneris CyYMBODROVG fi0.002 tierce wis is ae a ete ee oes 23
Asuncion formation, Vizcaino embayment ..........-- 31-34
Atajo Formation! | ..2 -.ss-ae es spac atau Boe od See 37, 38
Bahia Ballenas Formation ..................... 32, 34, 35
Bahia Concepcion Member, Infierno Formation ..... . 82, 83, 85
Bahia de,Guadalupe <2 .02 22 ocn G60 72, 73, 100, 104
Bahia las Animas ....... .. er eee ree: 72.13
Bahia Tortugas, Vizcaino embayment ........... 9, 28-31, 35
Bakers Leomecten 65 a8 woe Sin ce ers eee sivas. 80, 97, 104
Balandra breccia, La Paz peninsula ............------- 96
IBGIGNWS RTE BGTIUS sige oe a Son. ane, wa lord Sheed DR DOGS OSS 18, 24
Ballenas formation, Vizcaino embayment ........-..----- 32
Barrett Canyon, Salton Trough .............. 58, 59, 64, 66
basalt of Rancho Esperanza, informal name .... . Bi. 37.38.77
Bateque Formation oie cre cccus(e. s,s ere cecue aie over! s 32, 36-42, 51
Batequeus MeZquitalensiSi xs o.5 sha.¢ % @ ty skeueues e aysla yey 40, 41
Bay (Point BOrmattony erences anadiedinass o: teateratet glerGrg, Sos.t She eas oe 16
belcheris POrreria eo ecvi.c 0 o_o Seas e epee eas ere atene tere aeagewads, 31
Dellus RPECtTEM IP ECIEM)) .jacaishiepeney yaar O08) haps oka 18, 24, 31
BEnOisStid Dilliner agate wi aietai sae Goa! tks Gontaye arebnoe. sy enoemersg yen 23
BU ASLLS GICUMCTULG TILE LL ie fre, etchant vue es. bard cara, Rass (eusigs ager eerneas foes 42
bigelowl, YBraagrudOsphaeray occ os ce Sea 6.8 aks wiapeneienehenete ae 59
“Black Mountain volcanics,” San Diego embayment .... 14, 17
Bogorovia veniamini Diatom Zone ............0.000055 42
Boleo basin: ¢ 2% ese sede 10, 66, 72, 76-81, 89, 101, 103
Boleo Formation ...... . icib tibiae! Shut aug =, (hasta RU ORE 78-81
BOLLV ITI e ee ocieiton oi6oc dais ts. 37S an, dnaK Gee ea Me 31, 59, 104

CCLILTOPTIIGG, sen tesa eeanes arn, GO Sth eile Ewes Gag o-t ade ee 104

HOLT IUUTLOTOD cai Kes MGUE sy 9H a, cee hase aise Sema eee 104

PITAVGeENSIS-ZONG eeNs ayevecte nn afte ayo OSs eee Ee 31

QTANIL ieee. foto enemnre asks: on 8, conetalons, keds. iva, meyewet weet eee 104

efiiet (tN ole ee Pee etre ce tran St 5 tat eet aie ee 59

Pig HES & its. tat ih SEN e ape ccs ale eee MN a ct er earn 104

MULIETL 5 bos zee S esecn, woes 4 ew Pas ASS spe eS 104

bosel, Flabellipectert esa, sh as siete e Gs eke ee esas ee 80, 85, 97

BOSE TUPTHCU A. <5 ees ain ont Seo ays a ne as. 8 ol ale 36
bostrychites, Spondylus. 2. 2.0.20 nae cares Cee a Ra 66, 80
Bouse embayment, Salton Trough ..............-.-. 57-60
DOWerSi, CLYPEASTER verso. = isis eo eeyarety aie ad see adarahe Gua aye 67
Braarudosphaera-bigeloww .. «634600. 0 acemeeneds see 59
brevior, Buliminella 0620005 6 0 es ease eae ea ees 104
browwert; DiSCOQSler a6 oa Bene eee i ee 61, 100
BUCHIG IOC Nasa ave ahas nar amtied ae, we! Sos otis, Giascia iy GER 17,32
Buenos Aires Formation ...........-.--+00 eee ees 18-20
Bulimina uvigerinaformis ios. oc 00 6 ios Bea Bones Hh eG 87
Bulimina uvigerinaformis Zone... 2... 2 et 31
Bulinitella. 25204044 pea Spee hte ee Da Beas ce aS Oe 104
BEVIOR. ce cocw gow ere 38%, 4-4 me SAE ENS, I ah Se Sahat: Se gion brie heat 104
BUTTE oo ovcite, cafe cna ds aah geavawa Pes EG-S leon ahs @ & Meamenerene 104
Buliminella ele sartissuma 0c 6 eg en ccna bs te ns 104
Cabrillo: Formation. 6 diets ec Gti tee Oe ie 0S Baee 14, 16
Calabaza Member. Infierno Formation ............ 82, 83, 85
Calcarcous mAannOlOssuls a. eaten twa cle nese eae ee ee 000
California Continental Borderland .................-. 8, 14
califormica, BOlVing scoid ced ins Se 4a 2 helene eee tee 104
GALPOTNICG POTUES mS a0e Binders aaahens $44 ehsbake hteur hae seem 86
CQLISOFNIENSIS, NEriUG Cais cite sees eco ie ee OR Hes Bs wee 23
GOIVA VATIONS oe in eyfe. cote aes ee rect ae vice, ean ee ete yee 23
GaMpantle x \scso secs dca ishing an bw aap oe a «Ohm hea Reems eee 50
Canada de Arce Sur limestone, Loreto embayment ........ 88
CANGIIS, “Aequipecter i. axe csicps aes ie aie tee ene) sim oye veneee 42
Cancellaria (Pyruclia) diadela ............+45. 56, 102, 103
Canebrake Conglomerate: 2262 o/..405 sae ie ee te 62, 66, 67
Cannonball member, Magdalena embayment ..........-.- 50
Canon Las*Cuevitas, Mudstone: cac.s ss ce fe a eee een 69
Canon Rojo conglomerate, Sierra Cucupa, Baja California
FEA een PO. AFT eae a Seema TD Y ce aie RCN ete 62, 68
Canon: Rojo: Faults 5 «5 ec/n fae enntenn te eeaeuei oie Geen 58, 59, 68
Cantil Costero Formation ...........-22-+2++++0++ 23-26
Cantaure Formation, Venezuela. . 2 .....00205506605 82 sees 49
“‘Capay” Provincial Molluscan Stage .............--- 42, 51
(GArFCRATOGON™ f15, 2 2 Ficlets ee ove cas 51; 93; 100
CAL SUSTIC ENS Wiecats, chev veterans et annus eee ey er ane sspears the 93
Wie@GlOdON -s s+.0s.<cisce ee fees eae a eeahe aps ete eee oh 100
PHONIC IIS cx eaten ca tices Ae aan reetel Ce em eaiee cine an setter ewan raze 93
SOKOLOWIE) Wei Secs eee reese a cir ate vie este aaa aes ere egy eee eee eee St
Carmen Formation 22425 0.60 680 ee wie ete wiclece bf ucts 86-88
Carmen-Marquer Formation, undifferentiated .............
Pcie een eas Sea 74, 77, 80, 81, 83, 85-91, 97, 102
Carmzo Greek; Salton: Trough «222. 0525 e<5% 58, 59, 64, 67
CArFIZOenSiS,. ANQAGrG™, © pb ..8 ce lene is eisee aes cwel ie eesila oie, es aes 103
CassidulinavGelicata’ aca se 5 oa ales Geo eee Sie eee 59, 61
Cassidulina, panzana 7's gues we ele sects cues e bysvora syst oue 104
Gassigerinella chipolensts .... . vagus wears s Gwe ee = & 59, 67
Caucellaria (Pyruclia) diadela ....6 256.54 com eee ee es 56
Cayuquitos Chert Member, Infierno Formation 82, 83, 85
Cedros ophiolite, Vizcaino embayment ..........-.-- 32, 33
Cercado Formation, Dominican Republic .............-. 100
Cerro Colorado Member, El Cien Formation .........-..--.
Seiay Stanetawav) 8.2 Ota. ais auenye Garces eee 45, 50-53, 55, 91, 94
Cerro del Chichonal sandstone, La Paz Peninsula ......... 96
Cerro del Elefante, Vizcaino embayment ............ 30-32
Gero la Bandera gravels 224.2% 20002 202 oe eo See oh 56, 57
Cerro Microondas conglomerate, Loreto embayment ...... - 88
Cerro Prieto, Salton Trough .............:. 9, 58, 60, 67, 76
Cerro Prieto Fault) 220.4 ais ea. ee see oS soe eens 57, 58, 67
Cerro Tierra Blanca Member, El Cien Formation .... . 45, 50-53
CETTOSENSIS, LVTODOCIOH te ci aos dare ie, os wl, oe, whos) os ovals 18
CRELOMGS<GYMIGsee chro hens eet ee taeal seueMa ia cureeecgeunesne= «rete 42

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 141

GCHIONEMICHINOSERY ace 2 6's wb ein Baa ees Ba BHES a Rae aMS 36
chipolensis; Cassigerinella@ scsi icis es sigoars 6 ee ee en 59, 67
TATE S 2 rere, eaeeca eae eee ace ere, ONG S ENS: WAN TIS wreck 46, 47, 103

MEGIACOSIOIA® tapers ooo esas SN ea, Se eal Dative lace Wig an ane 103

tamiamiensis, Chlamys sp. cf. C. 22... eee eee 47
Choyal formation, Isla Cedros ...................4. 32,33
Cibicides floridanus local Zone .. 2... 20 ee 31
Ginta:Colorada,.Boleo basin. «0.002 556 tise es Gece ew eer 80
ICMVCRILGE OQHIONG. aio save em soto Sn ivao et ie Ana a oven. 4° 42, 47
cloptoni, Pseudophragmina (P.) o.oo 50
(GlypeasteriDOWETSH a. S.avcy ena 2 wea RecN ae sé. wa wo BOE 67
Coachella Fanglomerate. 2.5: 6c ck ee eee 60-62
(COCCOLURUS PEA SICUS nn oi cs pac shard eNO shew wa Rage Sa 59
GOdaKIG OTDICULAKIS ..5. Tene ‘ep ctiisinss: peels Ba. ab eMebehire: 88 doe BAP 103
COlinénsis;. Durritellamimetes sniss 9 5 HAS tes ow wire ol SR 100
Colonia Progreso volcanics, Siera Cucupa 2... 2.02... 62, 67
Coloradito formation, Vizcaino embayment ........... 29, 32
@oloradovPlateaus oicc. eave evs: wrte, wi atavtuel aati s eee ua shone aod 65, 68
Colorado River: sic. a ee kh eee 8, 54, 57-60, 65-68
Comondu Formation ...... 37-39, 41-44, 79, 83, 86, 88, 93-96
Comondu Group ............0.2.05. 43, 44, 81-83, 85, 93
Concepcion Peninsula... . . 9, 44, 77, 81-85; Table 7, p. 82, 83
Conglomerados los Juncos informal name, Vizcaino embayment . .
consors, Melongena (Melongena) .......0.0000 000 eee eee 42
continuosa, Neogloboquadrina 2... 0. 6 ee 104
@ONUSISPUPIUS As fodiee i as0 segues B98 wavs ae awe dee aoa a ene) RNA ay Se 103
CoralligGcnama Orcutt oF oh os ee ols Ss aoe Se nai Se oia oes 23)
corals, Salton Trough 322.2226 scecs hoes ee epar a oi ete ea 67
“Gorkseréw Hill,” Boleo basin 2... 0622056045 60245 78-80
(Gornwallius:SOOKENSIS; h.dnies Kisce cee s Swe 5 Sk donee ara anevacanal 6 91
Coromuel tuff, La Paz peninsula .. 2.0: 00... eee nese we ee 96
cortezianay,“Aéquipecten sag shied dBase Bae ihe G 74, 80
Costa Azul Member, Rosarito Beach Formation ....... 19, 20
CGOSTALUS; (StFOMDUS® s.heo eb ote ite ayacah On Gis Rye SRNR wes ae 42
Coyote Mountain Clays, Salton Trough ................ 66
Coyote Mountains, Salton Trough, California .............

EP ere ehapes er che nde) dbuto ce ans areas 9, 58, 60-62, 64, 66, 67, 69
CT ASSUSSSPROS i i550 6ta, fs.conlata. Wo \o- eoae os os Gr au Sig ae gO Gee 56
Grocodylusimoreletivn geist. eens da cis. x, oo iyerk So 0) 8-4! and, heb si 100,
Cubitostrea mezquitalensis .. 1.0.0.2... cece ee eee 40, 41
Cuesta formation, obsolete name ................2200- 44
CUMMING: HELA CUM AMON! x65) 5.15.5 90.45 5 SIPs 4a we a) Meee weed 104
GUILAB ILLIA CLLR yes eb hia &ccscasiny 501a! Seay dl es a apie. cate aa a> peas OS 104
CUSHMAN MLETILICULING fa. 5.5.10, wuncs wee SS BE Boga eh and HOD EY De ww 87
GUSRINGNT NRODULUS! s, aioe akties ate ak Spd as a ean x Away e a 3 87
CYyathodonta: 2atunensis: 66 ince eiden suck 8 see Ee Ey ae 49
Cyclicargolithus floridanus 2.2... 00.6 c eee 57,61, 67
Cymbophora sp. att. C. ashburneri . 2... 0.20 ee 23
GYM aN Os SS ut Gy Ales sald dah Sueakatyaniaraiguiss ee Suey ond Sooo 42, 56

ChelOMa; SPs.Ch GYM) is soa. 5, se eas gets tostinggeg Ges Re Ss gree 42

POLIT ieee Nea at lta ee et Pagan iges ei icw Aah OS, eis eRe CaN ial aft rere 36

MIChOGCANEASIS, SPs CRUCYMIG. coco a: inks Ses Bees 56
dallasis ‘Aequipecten nie ss, a, B.eG pn eesssacan ep aves o. x08. 82 80, 104
Gariend, ‘Clementia 2 ais. sp sts SP ORMR eee tee 42, 47
Deguynos formation, Salton Trough ................... 65
delicata: (Cassidulina, ceca e onc oewa es nes aaa ws 59, 61
MECIaS MHOUMMAL OW. 4s 4, 2,<G.a eee. c.e, eee oe Re 18, 19, 20, 72
Delicias Sandstone Member, Puertecitos Formation ... 71, 72, 89
Delmar MOmmatiOn orct4ias ghee dace doo bee ee hae 14, 16
Delmar Sandstone Member, La Jolla Formation .......... . 19
AeMiUreuUs; AT LOPECleN lois chs 5 Weitere totes 40 wees 6 e's ane Gee oe 76
Denticulavhustedtl ZOMG: x, sa.c tele a apaecuera ane ese 4 8 ave svat ane, 31

IDENTIGUIA IIAULAY ZONES (3 pers fists eaters ines seo sel ees a 31535.

Denticulopsis hustedtii ZONE: 2 cei see ee ee 35
Descanso member, La Mision basin ................ 20, 22
CSCI FAK SODECIEM 220i ad) 6 bow 6 BMA ee 68
diadela, Caucellaria (Pyruclia) .....0.000000 0000 ev eee 56
Diartus petterssoni radiolarian Zone... 2.2... 2-000. ee 35
GlAtOMS: 4.2 4. eng) Shr aca she Sess awe EIS ee 51, 69, 91, 103, 104
GLATOMIE ideo scananaeala bandos are apenetats 31-36, 39, 41, 42, 99, 100
Dichocoenia sp. cf. D. merriami oo. 68
Didymocyrtis antepenultima Zone... 2-6 ee 35,69
Didymocyrtis hughesi Zone .. 1... 6.0 ee 69
Didymocyrtis penultimus 0.0000 ee 69
Gilleri, Lituyapecten. (isc accesses 4.4 ok Ry = 2 eee ae wae 18, 31
Diplochaetetes mexicaGnus.... 6% 3 joe os eas ea « feo an ee Se 93
Discoaster Drouweric secede ia aeseae 8 Sy Sia few eee en ad 61, 100
Discoaster sp..¢h..D: surculus 25502 outa ann penne oe 6l
AISCUS,, AEQUIDECTSR: lites. 3 Ra weataveve a/tea.chenevasa gees Avaieet ana 31
dutertret blowi, Neogloboquadrina ........0..00..00.05-5- 100
Eastern Magdalena embayment .............. 10, 46, 89-95
EastLake Development ...............-2...2..000. 18, 19
Eastlake local fauna: 2 s....<4 ee eiecs aoe oo wea eae oe 195 21
edwilsoni, Amaea (Scalina) ..........0..0000 50000: 72, 81
El Atacado pyroclastic rocks, informal name, Loreto embayment
ny oes act on, gow GAR dopsleR ca tm aesSf 2 MBL la Bae fg sanP as) ay ng a TS 88
EB) Batra \s.iaod ie Soe st eecererte io cust are tee crete ae oe tee eee 73
El Caimancito pink tuff, La Paz peninsula... 22.22.02... 96
El Canelo, Tuff of ...2?22?.... or Tuff of El Canelo ...... 71
BkC@arizal Faulty sy 2% oitasdee a 4c, Seon oe, ee ete eee 55
El Castillo member, Rosario embayment... .......... 25, 26
EF) Choro: Formation’... 6 36.2 sacha ee wks ee ee 99-101
El ‘Cien Formation) 22aic< sacu-s = 42, 43, 45, 46, 50-55, 90-94
El Coyote conglomerate, La Paz peninsula .............. 96
El Disecado member, Rosario embayment ............ 25, 26
El Engano conglomerate, La Paz Peninsula. ............. 96
El Gallo formation, Rosario embayment ............. 25, 26
El Gallo rhyodacitic ignimbrite, Isla Espiritu Santo ........ 95
El Mono Chert Member, Infierno Formation .......... 82, 83
EB) Pilpito Rin y Olt’: cans 2 icc a Suites, ahs fate dessins GustseenantoheN orisha 85
El Rifle, Magdalena embayment ............. 46, 47, 49, 52
Bl Rosario 2 i205 oe acs a ded deegiod a Godda Bee aa 23, 24
El Saucito member, San Nicolas basin ................. 85
El Troquero volcaniclastics, Loreto embayment ........... 88
elegantissima, Buliminella . 0.000 00 ee 104
Elphidium gunteri:.5.. 144 seo eo go oe eh ee Ba gene Gea 66
BISIMOTe TAULOs yo ceessesyarseend: sn siectay ay artis cant ereyajterasens, onevere 575,58
emerson, ACGNIRING ss oe else ee aye Ge Bh 5 a dyn eeeOR 24
Emiliania annula‘Subz0ne) ice See es os pow add as ten ses a 19
Enicope Shepherd. see-saw. siscass els yove Be wi 5 © «Ries WEES 74
Ensenada ie.) sa avis es emalitvts ectbesisanie io Gav ate laa anaes « aeaane 2ges
Epistominella reliziana <.50522 205286 cna Sen Dam ees 104
Equus (Dolichohippus) simplicidens ....0.00000 000202004.
es MODE Sep hree Let ahneh cole Haven, BUG hy Sp ade GeGots ea Sidaris Wouter STM ere 100
Espiritu Santo volcaniclastic conglomerate .............. 95
EFugenia Formation... 2.4.0.5. 00082.s0 0054 oee Hs 29532
eurystoma, Homalopoma 2... 66 23
PUVONG 0 5.6 since ead es oe eee 49, 47, 69, 74, 80, 94, 100, 102, 103
REEDU os s).cd Bad ievane eqnepaner a soe 49, 69, 74, 80, 94, 100, 102, 103
TEPUBIOCNISIS~ S:5 Riek at eae eal ws Gave Rms vaeins 100, 102, 103
SPiy Sieg aha pies ererene) Sacnsasacos. hase sells another enn ony arene mercies: RNS 47
extremus; Globigerinoides . ci ei eae ee aa en i end 2 aKa 61, 100
faleonert, Rhvnchothertion «.¢ «ss, che 3 52.8 4 wae we tie Hage 100
fasciculatum, Pseudomussium (Peplum) .. 00. 00 ee ee 80
Felis.) LACUSTFIS: hn x 4505 6 oA SES oro aE yas oo Pe SewleeeponsaDe 100
Ferrotepec Formation, La Mira basin, Michoacan ..........
Ba Ase Seah Cay Rayer Garth Hy SPP raven ehnedemaiyn Seat 56, 58, 59, 100

142 BULLETIN 371

RishCreek (Gypsum: « j.. 2 scrcaw guerenee sue senna apenas 62, 64, 65
Fish Creek/Vallecito basin, Salton Trough ............ 60, 64
Fish Creek/Vallecito Mountains ........... 57, 59; 60, 62,65
Plabellipeciany ose estes teins po eens are 4 ae se eee 47, 80, 97
DOSED Am col aie; cere arias eens dus Spann ee eet 80, 85, 87, 97
PAMMENSIS “Saas a dns G52 noe hayes ae ein wets Ge axe neha. Bee 80
SPs ye ate ies etekny Poaetnd she fackatape rte eres en sietevien £1 sicatfernaher ay ata raits 47
floridanus, Cyclicargolithus .. 0.6.0.0... 000 e ewww eens 57, 67
Foraminata, BOUMING ions s canals avyess a Maes oti a,9 eel sees. 104
POVIENIG. cose. ba eb eee ee eg eek Pein tee oder eels, oes 8 ee 31
DEICH ORT orc: suspends ger aeand Gwaun! peeadte Fighecacde tion toe Glade ate 31
WHR tii Oo5. co a ahstiuns es Oho & Hdl dcbah BIEMS Boers oS wher oanle a es 31
fredeai, Turritella abrupta ... 0.00000 .6 00404 ee ee» 56, 100
freshwater mollusks: 3... 60000 0s ee ete mene ve nee es 8
Friars FOrmation:®? sicsiwcdsossiina geulae Soba akl aces ad fae 14, 16
galeatus, Strombus (Tricornis) .5. 06 se i ee ee es 76
BALEROSL, LV FOPECLEM . sNecia ca, tiyaiatcarts psyay eps. sissy Bite ee? @ Keres oh 30, 35
Galltherina uvigerinaformis 2.6... cee ee we ee 104
Gattn. Formation; Panama iciis iii a cid Fe ele oS ee os 100
gatunensis rhytodes, Turritella . 0000 0 42
patunensis, ‘Cyathodonta s «vcs eae sees Hae He HR SE 49
gatunensis, Flabellipecten ... 0... 00. cee ees 80
GIDDOSO; AMPHISIERING cass oecalsctea aya Stas 8 ea 59, 76
BIDROSO: ROGER | 5515 Goe. 559-8 35% lw Rp tient, Sodrgece Wher ae! Bhbae ee ee 48
MTESCIV EER « Cov ala. din), eae tig Gries wigin Se eS aaa oy ental A Se 50
KSLOUV REFINE wea kets “a yong ee eit 8 a ay PD AES Body eee eee 61, 100, 104
AN SUSTIUNINUICANA 5 5 rags cas Ghee gos = Spacer ae Pe ye Be 100, 104
MEDENERCS Sf. seid G8, B-G2% Setey aay Hae goniee sue, ene a ose, 61
pachyderma inCOMpia’ is wai wave Ge Hd we PS De ee See 100
pachyderma pachyderma . 2... 0.0000 ee ee 100
QUINQUELODG: crak bees abate APS wire Toa Reese a ss Mie BROS me BCR 100
GIGDISCTiRU appr: ethic be Shere eRe the, Gav aise, ase ake ar ane 93, 100
LO LTADIPICLLCL Matra Revke tere pee a8 Teylioo CaySrial tanga) (et SAN canto aye: CE 94
PEVULLCL MR Ot ee Sho cabaee Ree, eana at paras weoee ond trace AN Te 94
TAVUAL TAD UL LEA aver a aera Ne a wanna a) cae het ad) ean BS aes 100
GIODIBEriNOldeSarmacs cetera aan face%an eters Gietene o°4 61, 87, 100
XIN CTS ae ele, RUE A eee 3 so) -qiree-ay areas ah SANT) Rear ites some: ie Meee aie 61, 100
COD TITAS ieee rete a.niom, Weta ist eacaiel ahens, ae alscaane.a).epaAe 4k Ope 61, 87
UDOT ra Spates SATAN ENE, Saeenenantigetan's sete eed Hicks oy lk adhe ame Oe 100
Globoquadrina humerosa. .6 0.5 6 nab eee es 2 as 87
Globorotalia, «20s, «sates age as WO we wha ae, BA 100, 104
PENSUGEMSIS Ore erkae eas ante. Ba eT oe eee ee 100
TRAY ORT og 5 Bk Sica ces so eenis vnrdjetde lieve ale) goer Ale Asien ous 100
SCHL SCLIN sient ara bhinaand tate ateie ss tet eee 104
WIAD AEROS pei aad ie arte ak ae 6 weeny wee see rer ae 104
GlODULBerING OXfOFdIANA! voi i550 siecace: ced sees ae, Hee aw) Hee 89
Gloria FOLMMatlonl:<cccfeiieeee evn os, are ai ete Nels Ss ee vee 80
wlutinaia Globicerinua is os a0 nace aaa ene a ees SO 93
Gran Canon formation, Vizcaino embayment ......... 29; 33
PRG TROL ATIE ny. ovna. fess ceceaub meee. ee awe as een weeks ae ae 104
gravels of Cerro la Bandera, Arroyo la Muela......... 56, 57
RI CLALLUS PBALGNUS a. .mehoneachetenieereaseaeladeet =e eee nnn 18, 24
Guadaltipe Pasi: sc0i.43.@ Gua (otras dn sam Seekoue Ole See 72-74
guadalupae, Bolivinad 2... 0 0 ee 59
Gulf Extensional Province. . 2... .is88 s0 es 8,68; 71, 735 '97
PUNLETE CE LP HIGUUM teaeher eat 2 fvenels gerd aud Bon1.8 Ge ene bal oy seen 66
Gurabo Formation, Dominican Republic ..........0....2.. 49
GyKOLIRES me epee Maks «ih che alle, sab /esa ids, 2) eaensyonehes 78-80, 91
haitense: VASUML as iscv ME IS ahe sls ds Gere te ae ea. Slave 56
RAILENSIS, “HIYOLISSG™ 5, wares o) Gade wdalehalacs wee eG Sees ele eee 42
FIQIODIG INE GIG. ranais sid erae Side a angie eleva, GeO Rue aye Bbw Fa a 35
PA GLO DIG ESD ep. SN ela xn, base oes seotewes «ce: of NEE es ad ener sate 34
Hansensica multicarmeraia <0... 6 src egies as we 104

Hantkéeninanuttally Zone: .a..0s «bt Sin ens Res 2 De ee 50

havimianni;, MACKOR ca, iste oe Ferd an iensas's ayia ps ow iG, ene mate 36
heir; GYMia oo. eae) eye: crss, wee Solera eRe, Bade oe the ew wma 36
heteromorphus, Sphenolithus . 2.00.00 00 ee 57, 61
Homalopoma euryostoma o.oo 23
Hornillos: Formation ..2..00.52 2084 ee Gate sn 81, 82
Huertitas formation, Loreto embayment ................ 88
RUBRESE BOVINE «5 pn e 0 oot te, ees tO ae eee ea id ee 104
humerosa, Globoquadrina .. 0... 20 ee 87
RYOUS: FIVOUSSE <9 xo cs aro ae dy Oa ele en ates a Oe we HOS ee 80
FLY ORISSG o3e. 3)3. iacieeae bArB eat ane ao eval ae oF dys Baw PIS Re ee 42, 80

TGULCTISIS | = raion teed nee vo Geen eon te) ok Oe even ot sors eee em 42

DY QULS ores aceaat ethene iap stents enaihsiaetaa at oth aya Way shan aiowie et anahcts tances 80
Hypolagus: sp.ich. FL, Vers. «ics denis ows sistas Gn tle ebeeces 101
idriaénsis, OStr@@ sé ssc bitin eave a Re ORs mE ES 16
Imperial Pault. % hccnce wie kei d cee thst Sop eae ee Beare 57-59, 67
Imperial: ROrmmatlon.. si stece.0 eos Siew tect endl 57, 59-68, 76, 100
LNDEFIAUS; RAPGNG 4 o.oo Stig % 6 = G5) SPes ele ARRON te al emeuee 42
imperialis, Turritélla@ sic ce cies Hoa a Bee 66, 76, 103
Infierno Formation .............. 77, 79-83, 85, 87, 89, 104
infragranulata pachecoensis, Turritella 2.0.0. 00 ee ee 35
Isidro, Formation? 25 ccnlecis oc. card Gin b boateleieles 37-43, 49-51, 94
Isla Angel de la Guarda ..................-. 9, 10, 72-74
Tsla‘Carmen «256 2 ee gc ain hs Stim eld we sad ener oe 9, 84, 86-88
Wslav©edros) hs lotais ces eee Gah we dyes d 24; 28; 30,.31,,33,,.34
Isla (Cerralvoy sss caer + n8% 9, 67, 74, 89, 93, 96, 97, 100, 102
[slay @oron ade es. iy5.it awinae Sino. ayers cee par omen) mene ole temenete 84
Isla Espiritu Santo and Isla Partida.................--- 95
Isla Magdalena’ «i... sac 2 gate sisi eta es chains Soe 46, 47, 49, 52
Isla Miarganitac \s.5-4.6.%.c... 05! eeveereretgee mlerensy caeiep ones 46, 47, 49, 52
Isla Marfa Madre: cissitinc2 deo avsls ono tsps rene foe eee 89-97, 103
Isla Monserrate: 05.5.6 s0c.2.chs GG ores ae oes eosne Sra ep sreratiesstes 9, 84, 87
Isla Partida volcanic complex, Isla Partida .............. 95
IslavSan Esteban; 'S Ono’. <:..dehate = fgyenes cere ener Meceisete tw afsieeie 73-77
IslatSan: Marcos) ..02. «wate seers ae ane ee yeeros 77, 81, 84, 87
IslacSansRorenzo! s:i:.., <eeucnee aarisnue =] eeegeue anatete ai aan: 72-74
Isla Tiburon, Sonora .... . 9, 10, 57, 59, 61, 66, 72-77, 101, 103
Islas Tres Marias, Nayarit ............. 9, 74, 100, 103, 104
jeffriesi, Ammospermophilus .........0500 00 ecu eee eee 100
John Day Formation, Oregon... ..5...000s0 00808605 19
Keepin EUvolats,..cwon sarah 49, 69, 74, 80, 94, 100, 102, 103
Kreyenhagen Shale, San Joaquin Valley, California ........ 39
La Bocana Roja formation, Rosario embayment ....... 25, 26
La Bonanza rhyolitic ignimbrite, Isla Espiritu Santo ....... 95
La Buena tonalite and granodiorite, La Paz peninsula ...... 95
Ta Calera Formation i 4.csi0s 2cete geese eno eteccn ae een er eels 99.
La Costa ophiolite, Vizcaino embayment ............-.- 33
La Escarpa member, Rosario embayment ............-. 6, 25
War Jolla (Group sso ete Se ee fe Sloedls, wc apo 14, 16
EAU) OV a eaenreeta cemeteries tem emcee tts eenen- Seg cee eeme nen ecco eee ne 14
La Mira basin, Michoacén............... 9, 46, 54, 89, 100
Tale UT SIOM gy eeeerene Mors eaeeauetewen spc trraiterien sue weteseaetes cr eens) nays OF 18; 22
a Misién basin: cect: 2 2a oe 10, 18, 19; Table 2, p. 20; 22
era MaSionelOGal faunas: oe sen-geresircenamenase ohare) strove eftowerettanaeans 20
La Mision Member, Rosarito Beach Formation ........ 20, 22
La Palmilla gabbro, La Paz peninsula................-.. 95
La Paz, (Crystalline 'Complex 2 awa sar. oe wee we soe es DOO
Ta Paz Fault. oii ne 265 oe = bgt leg Scena dle ret ors ante 54, 95
la Paz tuff, La Paz peninsula: ss see. wer. «22 ee DO 92-90
IAMPUTiSiMa tere seenuereeee attention eae 9, 38-41, 43, 84
La Vinorama conglomerate, Loreto embayment ........... 88
NQCUSTLIS cRGLIS2) te: srecayues winoh onie Wey kee Caen nd emeheaeme: ease emer 100
lajas Palo Verde, Magdalena embayment ............ 45, 51
Las Calaveras tuff, La Paz peninsula .............2++.+. 96
Las Glorias Member, Rosarito Beach Formation ....... 19, 20

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH 143

Watrania Formation: . <2. 208050 e0G besa we eae SO 65 Minitas Formation. .21c09.5 incre ece)aca, a and Gade ater s Guae-aiehai 81, 82
Latrania Sand Member, Imperial Formation... .... 2... 66, 67 Mira al Mar Member, Rosarito Beach Formation ....... 19-22
lenguaensiss'GlOborotahia <.iiie ec cn ws 6 wien 3 nee ee Hee 100 Mission. Valley Formation: ..ii cnn ee aa Se eae eae 14, 16
Menticulina: CUSAMANL) Mists. bse % a. eed rane hg ee Ge Ia. 87 Monotis sp. cf M:. subcircularis: «04.656 8 Sais wo, ale ee 35
WeopecteniDAer i: Veni. aah she nts roe he ais oreo WS ee i 80, 97, 104 ““Monterey-Beds,” Purisima-Iray basin ..............-.. 42
ADI OCH CIING! SHAVE uxt airs, a eeherem eee ipo lsuc Gi etaciia eeeay ens 41 “Monterey Formation,” Purisima-Iray basin ............. 42
Mee DOF UMETISATTITULATIG © & ihe (e 5: apes: 3 yah Sneha: Bs vans BiB ews BLS 49 “Monterrey Formation,” Purisima-Iray basin .... 42, 51, 91, 94
Meptopecten praevalidus: ais. Gina Sei eo eed we ae a cen 31,.35 MOFELELL, , CTOCOGY US © az.shavts a, ansible yrs o. nso sieel ets seer 100
Lindavista formation, San Diego embayment ............ 16 Morro Hermoso ophiolitic complex, Vizcaino embayment ... 33
LiM@Gla, MAGIODIGS arate o-ata es ean oa egg ae de Wares seer 35 Morro Redondo formation, Vizcaino embayment .......... 33
TeityAPEGlErWAd Lert 2 o Grencc ere, crea oiow. ails.) SbisesNd 6: 4 ates Ges 18, 31 Mount Soledad Formation ................00-00055 V4: 17
Llano El Moreno Formation ..................... 68, 69 MULLET, BOUVING: 62 sun airs Siena at Bare VES OD Miu 104
Lodolita Arroyo Amarillo, San Nicolas basin ............ 85 multicamerata, Hansensica 2.2... 0 ee 104
Loma del Tirabuz6n, Boleo basin .........0.00.0000. 78-80 Murexiella (Subpterynotus) textilis . 2.0.0 00 ee ee 80
Lomas Las Tetas de Cabra Formation............. 24, 25, 27 IMUSCOSUS, AGQUIPECIEN” “soit cia len a oa6°@ Goare eid Scene 76, 103
) (0) o 100 ee ee ee 9, 43, 44, 84, 86, 90 nelsoni; VeneriCardia® <2 15. 6 c.sacv sig selene Rtue Ghai Gis 2 ae 35
Loreto embayment .... 10, 68, 74, 85-91, 94, 97, 100, 102, 104 neoabies; Sphenolithus: 22.20 0cscte ed eos eee haw ee nes 61
[os Angeles basin. . sn eet ae te ee eee es 10, 18, 22 Neogloboquadrinad 1... 0.0... ee ee 100, 104
Los) Barrilesi Formation : 2.65 cnc ds ee ce cee eee oe 99-101 CONMMUOS Gos id. ai ania bm aie ae aa eee oj Ee 104
Los Buenos Member, Rosarito Beach Formation ....... 19, 20 CQUIEFTFEL DIOWL “5 «3, das 2. seeenn toh Wrostaist ahanehanal apsttweta te etme 100
Los Chapunes formation, Vizcaino embayment ........ 29). 33 nepenthes, Globigerind 25.0044. .00005 eee eames st wees 6l
Los Cuervitos limestone, Vizcafno embayment ... 27, 32, 33, 35 Nerita Californiensts: ccc. 6 aecea ee Sav a RR ERR Re 23
Los Indios Member, Rosarito Beach Formation ... 19, 20, 22, 31 Neritina luteofasciata ...........000 ee ee eee 100, 103, 104
Los Juncos Conglomerados, Vizcaino embayment ......... 32 Niguel Formation, southern California ..............-.. 18
Los Pargos formation, eastern Magdalena embayment = 89, 92, 93 NODILIS; -APCRITECONICA™ Fnaucte fons 's. saskern pane. gered Texas ee ee 56
Los Volcanes conglomerate, San Nicolas basin ........... 85 INOGIPECtEN! on Sinead am ahs, Bo SAK So SRN Ie eens 80
TEUCINOMA SANCIGECTUCIS. Skew setae t whe ee ee wale Mee 31 MLOAGSUS), oie torcsice, less ys (outs. coda teks, conan al Ges eMC ee Une 80
usardiFormation. cose ste sce ccs See ee des 14-16, 19 SHDNOGOSUS. 2 o.0a.ace 298 «BS uo acee A ewe as eee nNOS 80
lutéofasciata:, NeVWING «26.04 cic Ri ee ae eo 100, 103, 104 nodosus,..Nodipecten: ... 6 ioe es fa ed ee oes bd eee 80
PYTOPECLEN EOE arevsed Sli ate tte Sa e se eS 18, 30, 35, 42, 76 obliquus; Globigerinoides: «02 4.222.280 6580 nt Bale Gee 61, 87

GETT.OS EMSIS: Bits ofan ativens aid) steed dcaniodrele 3.5 eis slontis. tae eee 18 obliteratus, Strombus. iis ie bs na ene BR SS 66, 76, 103

RAUL E BOSE Mas crtz Naw eteayiaict ane Re a) aut ova eudee me Bee Rae 30, 35 Occidental Buttes! . 2.5 4 2 + kkietae se Badcte eRe Se edie se 24, 25

PRTELLOSUSIe site Wages ase S ape siuenGs Ste wn slee ens! Ae fone whe te ease a 42 OCOVANG,, TUTHiLEll fesias airx Bzbse ena age wk ae, Giah a ovate ae 22,31

LEDUTONENSISI Rad ee Meee, Hae Bd ete Ces o a See Oe 66, 76 Oppenheimopecten VOgdesi ..0.0. oc nce 6 om and Evia ie ee Ne 104
IMACTON RAT IINGMII Biota, oxo: tteeheidiie 1a, 3a Melis ei.e: Bags 6 ow 0 36 Orbicularis; \GOdQAKIG 5 a..6.als Be Pi Soe eae oe nee es 103
Magdalena embayment ............ 43-55; Table 5, p. 45; 89 Orbulind SUtUralis. (creep a-s: tesvde tear eves. sist oats ev epee 104
MalarrimoJFormation 920.7. .ccs ees cusne «aces ee ens 8 ea we as 33 OVCUuttl: “COPGIUACRAMNG .cavaceie eons Soe eee de SLR ee eee 23
INANILIMUSMRODCNOCUITE Medien ist. 2 Cites NOG eos FS ols Die. 25 OSTEO natetcineste eels ia st veer aie hvac seme es 16, 68, 74, 104
Marquer:Formatiom ies 206.506. shecpie stele 4 Ha a 86, 87, 88 IAPIAENSIS: ¢ feo 5 he be Gis ee ee eo eRe oe oe 16
Matomi Mudstone Member, Puertecitos Formation .... 71-73, 81 VESDETTING® .rayssvgnd Ga -w aeabie newer aes ace, HS oe ee 68, 74, 104
MG CTU AGIODCTOLGLIG? vg aa at a niearan shit eetets a eoNe ug ai Ne Ble vend aod 100 OSITER VEGICHEE 6 io ea ane aces. ae wigs baie aie av teeal ns Shanees 31
mediacostatasGhlamys an ais 5 2cle 3 ta eels 26 a a eee alse 103 Otay formation, Tijuana basin. 2.022555 22s te eee 18-21
Medio Camino member, La Mision basin ............ 20, 22 Otay Mesa, Rosarito embayment, Tijuana basin... ..... 18, 19
MELALOGONWGATCHATOdOM oe 6 wise tunings Se ke Fa ee ee 100 oxfordiana; GlobuligerinG s 3.0 6 casos @ Hels Oe see eee 89
IMCLON RENAN Gi a axcio sete w sis Mace Dis ea weal eed we Be 42, 100 pachecoensis, Turritella infragranulata .. 0.2.0.0 62 oe eee 35

(CVelOn SENG) KCONSOMS® sis. 2. ope is Shine) a Somlny che Walz dete land easels 42 pachyderma incompta, Globigerina .. 2... 206620 ee eee 100

Melongena:sp: Ch.M: Patula@ <x. cis enn oth MOS ae eee ee 100 pachyderma pachyderma, Globigerina .........0..0.+5- 100
Mencenares volcanic complex, Loreto embayment ..... . 88, 90 Pailebot augen gneiss, Isla Espiritu Santo ............-.- 95
merriami, DiCchOCOEhiA iis tics Re ee See es 68 Painted HilliRormation”, .;. sacchevg g's sss levee tame 59,6163
Mesa de las Auras, Vizcaino embayment ............ 30-32 Paleogeography of the Baja California peninsula and ancient Gula
Mesa de los Indios, Rosarito embayment, La Mision ba .. 18, 22 OF ‘CalifOmmiars scons) ocre scenes ce eaar a seal eee a eres Gaeaae 54
Mesa el Tabano, Puertecitos embayment............. 70-72 Palm Spring Formation <2 a2sasgo30. 00004 seins 63, 65-68
Mesa el’ Yeso, western embayment ....... 0.0 6s Bees 37-39 Palmira conglomerate, La Paz peninsula ................ 96
Mesa La Sepultura, Rosario embayment .............. 23-25 panzana, Cassidulina: 233.300 ous pe amends 6 eee wows 104
Mesa San Carlos, Rosario embayment .............. 24, 25 Paraguana Peninsula, Venezuela... 3 sus... 6:20 2d Steers ein ae 47
Mesa sandstone, obsolete name ..............-..--4-- 23 patricia: ANGAGG 5 .osni\ ar aah a nua s Rae te cy, say sucha ENN © eer N SR 100
INT exaC alii gey pen a ke penton ita sete StS TAI Merete te ee dienes 9, 58 patulasMelongend® ste aiersie fave, BRStee aia) o-0) anny Secu ct ele 100
MeXICanuUs? (CAnChATOdON. fs wo Dspace oe ais FR Oo ee 93 Pecteni@letes: cea: wsvary a ate ileta: dea a acetate are Sane ea ey ke 100
mexicanus, Diplochaetetés 9... ..005 vie ee ee ee 93 Peéecten.(Pecten) Delius. 3, Sar. c wt o-c ae ke ete oe SPN 18, 24, 31
MEZQUILAIENSIS BALEQUEUS: a isristi si cae S a ewes poate edb Batis 40, 41 pelagicus, \Coccolithus’ Fic aa ais seas st oc gun eee akan een Se 59
MUCROACANENSIS, GYMIG: sia. date sects ar eis de Sy Se ahs oss Seale 56 PelonéssHormation® its dia as oare geet are tels weet re ee ere 81, 82
Midriff- Islands; Gulf of ‘California! is <i ..2 ec ae eee 72 Peninsular Ranges ............-- 9, 14.23, 35; 27; 57,.60,:89
WVEELERGESCATTUST roy en oreifo iattaonas UAT Sek EONS oNie) eos sols lake ane Seles 18 Peninsular Ranges batholith... . 222. ..000.8¢28 005% 19-24

Foieh Vis guphiemies @ Sbelohels Steaua eeshene 100 peninsularis, Vurritella (s¢ 2d ssp. a.we-cte) des eee eke LOSS

144 BULLETIN 371

pentias Penueua cciiis a8 si Shs ne Re oe eae Bee alee alee 25
Penitella Pena: cine eres ost ar ha aa sm a ad Sa as NS 25
DENLAS;, SPONQASLET 22 woo = Sia hn 8 4 Fw we Ee ane Bene Bo spew 69
penultimus, DidYMOCYTUS ...< s.0.s000 a Mies ie Fae Be RS oe 69
PenCOTUS, ATBODOCLENS 651 aie em Bene Sralcunmal, eve sakehee 31
DELETING, AMIZETANG 2 vsiccr's, axial aa, aycvis tan'eres |=! spay aja oyd ous 59, 61, 69
Perforada sandstone, Vizcaino embayment ......... 29, 33-35
“Pharell sGUG. \ cis ss ome' ce Seems ara tattrw ood wre al ae eee. ok en 16
PHOS Spi Gh.iP> ChASSUS +, 2) osc aaahs' otis bias a1 s'9 epsadi ara atecats 56
Piedras Rodadas sandstone, Loreto embayment ........... 88
PilanesPOoMALtLON < 4.<rc.c ceed ayevice e but Gee Sompeshars aiayevare al a 81, 82
pillingt BenOws tid 5.2 se wes seta. a Ss 6 ees a espe Mens ayes, pie
PinOSMBOrmMatiOMs <a) a vas, Se H Soe ash ate tere a cise an anes avara, 2 33, 34
Pinta Tintorera basalt, Isla Espiritu Santo ............... 95
LOCH; IBUCHIG a5 foin keds teed alanine Wp duets oP se By eeeyieal ae W732
PIGQCUNANOMIA CUMING ors eo.% oe dae oh Ste SA ag Heres 104
Playa: San FelipetGroup ici. cea tees bP ee 8 68
Pleistocene «24256 8, 23, 29, 47, 49, 74, 80, 85, 86, 93, 97, 104
plurinominis, “Ae€qQuipecien” ac choi sateaa tea aw aes 2s 66
Point omarPoOrmawOn 0.5 c.cere Gyene whee. ole one, wietee we ony 14, 17
Pomerado Conslomerate® ics iiss Godin Gwen wos Oe os 14, 17
POPENOCUIN TNATILTAUS 6. Faia G3 wit 9 35 te hd areas Bovine, 8 eTS a 25
PROFILES CALNJOTUICAs %, s iisvat tjerey eee auaus.duaueyeveus @ she Sai, = he Gu Sms 86
Poway Conglomerate .... . wis Sy Tene oie rood) «ee pike, sh.gue Sues: Gyles 17
Poway ‘Group Pisses Mee se ee om alee be Stes 14,17
Pozo Iray #1, Magdalena embayment ............. 41, 84, 85
Pozo Iray #2, Magdalena embayment ....... 47, 52, 53, 84, 85
praevalidus; Leptopecten sic < oe cise 65 0 oe so 8 aU 31,35
pretiosus, Lyropecten ois ne ers Hanes ies ae ee Hoe 42
protogulf.of California. .05 o. cco ee cee o aheletsts 8, 54, 76, 101
Providencia Rhyodacite’: 22,422 Sicn2 eo osgide Sain ae 95, 96
Pseudamussium (Peplum) fasciculatum . 2... 0. ..0200255- sO
PS CUudOPAFAGINING rensrraeusneucten eye tne ka.'e sxe cena Sec as 41, 50

(Pseudophragmina) Qdvena@ os 5.00.00 is esis iene 41, 50

(Pseudophragmina) cloptoni ... 1.20.0... 0500 eee eee 50
pseudoumbilica, Reticulofenestra .. 0.0.0.0 00 2 ee ee 59, 61
Puertecitos embayment i... ehc = arse cuss © a yetn csi i's 10, 69, 70, 89
Puertecitos Formations :: sc. 5 fies ce gt en aed 71-73, 81, 89
Puertecitos Volcanic Province: 05... ae sls's.0,6 5 20k ete ee te 70
Puerto Escondido tuff, Vizcaino embayment ............. 33
PuntacAbreojos! 5 6.46 654 oe ce fe pees 30-32, 34, 35, 37
Punta Baja formation, Rosario embayment .........-. 25;.27
Punta:Ghina).. sc oS stan o attie 4 die ew = ote ele & samt swe 23
Punta Chivato: 23.652 052 00). tvens pee SHE Hees 83, 84
Punta Coyotes gravels, La Paz peninsula ..............- 96
PiintavIDESCanSOr aoa ssyeuaa « ccen «ito muete ee pushy ateee cedcae 19
Punta BuSenia. so fe 6 fn ee & siete Poets ee sees whens oe 29-32
Punta Lupona volcanic complex, Isla Espiritu Santo ...... . 95
Punta Malarrimo) «2.5 sc cee bc ee Hee ee ee = 24, 31
Punta Maria limestone member, Rosario embayment .. 24, 25, 27
Punta Mesquite member, La Mision basin ............- 21, 22
Pinta: Mata; Nayarit: iyi os asus ¢ sos, acce Seeuads 9, 76, 103, 104
Punta:Paredoém Amarillo. iii 6 se eae ie Sees Ae eras 83-85
Punta Pulpito ..... «saa origebaa baieawy Me Ganesan e re aes ae oa re 9, 84
PintaSan Miguel . <5 <.0406.6 06 «0 seme o0 cae been a sete 22,
Punta San Telmo, eastern Magdalena embayment ..........

CE ee Se a ee ee ae 9, 44, 46, 84, 91-93
Punta SantayAmtomita s2 5 oicr eos. s) ors eRe rshone ey sae eke Gueeeiets 9
Punta Ventanita: sasnscc ae enews a ce cue ane Siege sare Slee ones 22
Purtsima—Iray basin ........ 10, 38, 39, 41-43, 50, 51, 85, 94
Purisima Nuéva Formation: 2.2 26. «ee ee as eck eiae 43
Quingueloba, (GIODISETING ‘5 ops eienstate @ se 44 ts ear a a als 100
RAC SI DOSa: Wada ehwel hn suas wir ose eee ene eat eae ee 47, 49

Rancho Algodones, San José del Cabo Trough . 97, 101, 103

Rancho Bateque, estern embayment .................-. 37
Rancho el Aguajito de Castro, Magdalena embayment .......

ards aa Sissi htaa tegen eis Mair. cats ahs ces msn ctechRskay Se Manche Sis aust saiaatys 50-55, 94
Rancho el Refugio, San José del Cabo Trough ........ 97-100
Rancho Esperanza, basalt of, western embayment ......... 38
Rancho la Palma, southern Magdalena embayment ........ 56
Rancho la Salada, Magdalena embayment .......... 46, 48, 49
Rancho San Angel, Vizcaino embayment ...... . 30-32, 37, 38
Rancho; Santa Be) aicaes says aa sete ao econ Ss ee eaeers 14, 15
RAPQNGWMPETIALIS « ai P a sacapates as, arenas! ays yeas tevsinancpahear tone ences 42
Réctouvigerind. mayt ZONE vic soe 44 4 Hla 0. oa Ae! see 31
Red Rock formation, Salton Trough ................... 64
Redonda Formation <2 6.5.4 s.00% «5 62 aie wee He 18, 19, 21
Refi sto Formation) 2. chs snare a awe cse th eteuahstsaeaver eile 97, 99-102
TEURICENSIS, FUVOIA. .is6 6. o-sint steal SR eons wale 100, 102, 103
TELIZIANG, EEPUStOMIMELLG six iac che sigsy sein, 9.50 ce). Hea) Savi) a ete Pe 104
Reticulofenestra pseudowmbilica 2.0. 0 59, 61
VEVELIEL, ATLOPECIEN: sn icc ae 5. Gaye aise dos, btu eae 74, 97, 104
Rhynchotherium falconeri as a300 26s ve ee a wl ls oe bee 100
Ricas6n' Formation: jase casts Gyaeiientycievte Se ec es ewe 81, 82
FICRINGIERL, “CRIONG yiiete cow: < 49S. eS eee ae 36, 38
Robulus CUSHMAN sve cad dads oso Bh GS dhe aus kes 87
Rocella gelida Diatom’ Zone 42.2.5 2062) Fe wis Se ee eee se 42
Rocella vigilans Diatom Zone «2 2 6.44.6 6<.a we les ieee 42
Rosario embayment ........ 10, 20, 22-27; Table 3, p. 26, 27
Rosario Formation “review shee eee oes oe 19, 21-25, 73
ROSatiOv Group cs) «, capa Hares. y reac ckatee as secre eee nemeetes 14, 17, 21
ROSARIO Sri « ani Re ie ey Sires ane ere nena ete aan re 195.25
Rosarito Beach Formation ............... 18, 19; 21), 225.34
Rosarito embayment ........ 10, 14, 18-22; Table 2, p. 20, 21
Round Mountain Silt, southern California ............... 22
ruber. (GlODIGETINOIGES. .2 Gb kobe wo oe 6 ole as areas 100.
SQCCOMAYATACHNOIGEG a. ancl casita: ins as 5 1-avat es avauaa sysgeesnay er ane}enos ele 89
Salada: Monmation cs nce c.c:ce eese ne see one ohees stg se eweee eats

wee... 31, 37, 42, 45, 46, 48, 49, 53, 55-57, 69, 87, 95, 100
Salinas: member, La Paz peninsula. 2.40. 24005.5 522200: 96
SaltOvPOrmatlOn eqns eersvate ni reesneteta ne anaes 81,83; 85, 89-93
Salton Trough 10, 54, 57-68, 76, 89, 103; Table 6, p. 62, 63
San Andreas Fault ...3.:¢80. 208003 sea foo 57-59, 61, 64
San Antonio formation, Loreto embayment .............. 88
San Antonio toba, San Nicolas basin ............-..-.-- 85
San Carlos member, eastern Magdalena embayment ....... . 91
San Diego embayment ....... 10, 14-19, 24; Table 1, p. 1618
San Diego Formation 22 2 2.024 a sle cc elise ees 14175709; 21
San Pelipe a fac scmeus 6 oars panne sent tasty oes 9, 58, 59, 74
San Helipe Diatomites 2 os severe avec aco eepeers eee sy cee 69
San Felipe ‘embayment) 2s yaa 2 gee aus o) ware eer 10, 68
San Helipe mutt of mises eeeusseusectncsCavnahe hemes emcee nee ahaha 70; 74
SansGorgonio-Passijiiss gece a eG be ee ee 9, 57-60, 66
San Gregorio Formation ................ 39-43, 50, 91, 94
San Hilario Member, El Cien Formation .... . 45, 51-53, 91, 93
Santeipolito ese 2 a ane sues oschraerceeuenmeerenreemeten et tncce 30, 31
Sani Hipolito: Formmations, <i..1. ts. aectens 2) te aus chepe saya 34,35
Sanwlomacioya vac her nutels toe nsie ert ans 9:30) 32,375.38
San Tg¢nacio Pormmation” wz c.ccststagsuecsstine Go ans ac 31, 35-39, 43
Sans ISidroy arses cy crc | Ges yet eusene op mene eaemobete erene 40
SanjJoaquin’ Formation 22g) eos eonertersuey custarta)a cieuatteualey Several 36
Sani José de ‘Comondw): 25 22. sins oro ete ees oe 39-41, 43
San Jose del Cabo Trough ..... . 56, 95, 97-103; Table 8, p. 99
San Juan de la Costa 10, 44-46, 51, 52, 55, 89, 91, 93-95
San Juan limestone, Loreto embayment ...............-. 88
San Juan Member, El Cien Formation — 45, 50, 51, 53, 55, 91, 94
Samnan MUEh- ee aoe coos terse ve reeewe eta cepannesnaueietene eo arsusncie 94
San: MarcosiPormation, 5 cvauctees 2G eo ats aoe keene 81, 87

BAJA CALIFORNIA STRATIGRAPHY: CARRENO AND SMITH

SanNicolas: ba sit 4 ceca erapecatene tester ste gnstace bs aNenane "sees 83-85
San Nicolas formation, San Nicolas basin... ............ 85
SamOuinti sco apa seca awe a ae Gees ge le 23, 24
Sani Raymundo: Formation . 2... 2.06 eee eee 39, 42
Sanwllelmo (PlutOn 25.00: Bhs gle has Bodn es Be ae es 23; 27
San Telmo formation, eastern Magdalena embayment 89, 92, 93
San\ZacariasRormation’ 6. .a656c0 060i ec en oees = os 34, 36
SQMSUINGIATIGTOULQD 22. nq sotaascva aWen aris, pasue aha a soye tae) Sys yal he 38
Santa Anita, San José del Cabo Trough .... 66, 76, 97, 98, 101
Santa Clara: Formation’ <0... .i2ca Ss8 oe ses og be ee 34, 36
SantatRosalia) .., =.5%. son 0h ogee ao eoseae sh gies. @ Sheeseees 9, 77-79, 87
SantaRosalia!Pormation’ 2.2 cups santa o esis S eee Bo es 80
Santa Susana Formation, Simi Hills, southern California... . 35
santaecrucis, Lucinoma sp. cf. L. .. 2... 62 oe ee 31
Santiago diatomite, San José del Cabo Trough ..... 76, 99, 100
Santiago Peak Formation 0... 060626602 scene wees 14, 17
Santo; Domingo Formation. 2.20 6c swe k bees setae oe 41
scitula scitula, GlobOrotalia@ 26). sce discreet ee es 104
COM Ss POTLAYLUS.» Gameiias os aie ede 'S a1 eaves: OS wea Pamsuerave evs a Dat 42
SCopps POMUAWON: 2/5 6 4.05 Gla trie oa ee en ee were 14,17
Sepultura, Formation: <0. siecities cs yee oe Sacre 2 27, 3D
Sespe Formation, southern California .................- 19
SHEDRETAL, MENCOPE ia sharia) ae a iu iw hs apo ah oes use No Wests 2h 74
Sierra Blanca Limetone, southern California ............. 35
Sierra Cucupa, Salton Trough .......... 9, 58-60, 62, 66-68
Sierra de las Cruces granite, La Paz peninsula ........ 95, 96
Sierra de San Andrés ophiolite, Vizcaino embayment... . . 33-35
Sierra de Santa Lucia, volcanic arc rocks ............ 44, 79
Siemaide:'SantaRosa 2. oc<ic65.4 meas od Oe sees 58, 69-71
Sierra la Giganta .............. 9, 36, 39-43, 79, 83-88, 91
Siena lavlsaounats co: erie oes oles SAS coe a 9, 55, 95, 97, 102
Sierra la Trinidad, San José del Cabo Trough .... 54, 95, 97, 98
DIEIE AV AS VICTOR Abe, aero ie. or etsnsnsiaae i & erm Gut sien ® one 9... 54,95, 97
MleMrAa SANG REUPEH ers. Hise cpis2 aceite asus ous ob Sai Gsm 58, 68, 69, 71
Sierra.San Pedro) Martin’ 2.50.5 ce ee ee ee ees 23, 27, 58;.70
Sierra. Santa Ursula; Sonora 2252 sccca eee Sere a tee ees 75
simplicidens, Equus (Dolichohippus) . 2... ...0.00-0-55- 100
SOKOLOWI, “CarcharodOn: 22. eek ce ee ee Re Sees Sl
SOOKENSIS) (\COTNWALTUS. <6 ig se card esis oss weet oo sens. ee ee FF iene dra 91
ISPHENOLITRUS. Seven. shiee em Sie, Ais SAREE ge 4 a 37; 59,61

OLE SR Rene ys) sachin APM a Yara, BACAR Re So etaoeag tens Grants 59, 61

NETELOMOTPRUS Gis eraets QAO ee Ga ee Hoge HE thee glelsts & 57, 61

PLC OCLDLC Share Peete see bs cs \cecsi sy ators, absslygins sass si/Svava (sLaivsiyeregets 6l
Split Mountain, Formation ..... 0652.0 56.2e0800 esses 63-66
Split: MountainiGorge: soci 3 Seis nea Betas 59, 62, 64, 65
SPONGYLUS/DOSTYCRUES oo .0, 25.5 ieee Bote eS ee wis ease 66, 80
WS DOMGY USS COT Metin ce osieestse i ap 6d G-Star alvey,tyiehaevralsy en areuisy wi (elvtne. fe ae weg 42
SDOMPASTETDEMLAS! co eee rsh i oi tes vhs «40. 8) Sus WAS) Bosra ova a, Re 69
Springvale Formation, Trinidad ...................-.. 49
SDUTLUS a CONUS? erat S Sratnid ace Spits Bhs) HN wh RSS cue Oa 103
Stadium Conglomerate 2. ees be ese gee gcse ee saan 14, 18
VMEHOTRVAS TOTOEMS E28 eis im sci im Grapeseed m hee -e Ow eH ces 4 ena 87
IST OPMOUSH thay ehtue ta ccaete et 6, ay aa Ronee oralaeehec eee a: ise 42, 66, 76, 103

Costatus; ‘StVombus: Sp. Ch. Sis 3 2 os te ks ee ee ee 42

(Tricornis) galeatus Strombus sp. ct. S. 2.2.2.0 2-620 eee 76

ObUiteratus: sh Sogn thts ge Peg eee Se Ss 66, 76, 103
sturzstroms, Salton Trough! 106.600.0000 0060 teense 64, 65
subcircularis, Monotis: sp. cf. Mo o3 ssa. ese eee es 35
Subcostata, ANOMId. 32.222 60%06 name nce ee RR es 68
subnodosus: NOdipecten! 5.03 ci ee ees eS oe 80
SULT. CULUS SIDISCOASIET: cous. 3. «fo apd ates Oe. as Gp Ee ie He le Slane hens 6l
SULLIET; ILS s| OM DULUIOL pet crlotter cue eihaePea eae, eres) siete) Seis (bi bis Stectaiga way ad 104
Sweetwater Formation .... 60.6 2062se55e208. 14, 18, 19, 21
tamiamiensis, Chlamys Sp. Ch. (C@. occ ese shies 47

145
Tecuya Formation, southern California ............-.... U9
“Tejon” Provincial Molluscan Stage .............-. 36, 42
Tembabiche® . 0. e:¢.gc oGp3 5 ee sok ep ress 44, 81, 84, 89, 92, 93
Tepetate Formatio .. 36, 37, 40, 41, 45, 46, 50, 51, 55, 90, 91, 94
textilis, Murexiella (Subpterynotus) 0. ......00000 5000 0- 80
PRAIS: WIULUCHL 5,3 2s Sop Sa erp een SS Soin, F Mus race Be 36
Thalassinoides,; Boleo: basi o...305 6. nce. eosce Hs 2 6 ees dws 719
Thalassiosira-Oesivupit ZONE i022 copie eg Se eG he ee 69, 88, 91
thauina;ANQdQAra® 0s 6 505 6 10 be SS wie RSs od ose eee wes 103
tiBUTONENENSIS,. LVKOPECIEN aciisig Goad 2 ie 6 SS epa Sonata tie we Sais 76
Tijuana basin. 2 este ee ss 10, 14, 18-22; Table 2, p. 20, 21
Tim babiebis epee sree eaten cy yoke mseenevatee eae a sms 89, 91-93
Tirabuz6n Formation ........... 72, 77-81, 83, 84, 101, 103
toba: San Antonio. 25.22. 2 652.4 2 cides sue Bee ed eon cele eusawee 85
TOOOS!SamtOS wos. 2:eachersiere,snehemahes tue cers dour sles iscd Peekens te. 9;. 10; ‘55
Topanga Formation, southern California ................ 22
toroense, Sthenorhytis .. 0.0... 0-0 ce eee ee eens 87
Torrey Sandstone: 6 cigeccsreasevdhe a: eo co ecehamevane ee erecaue suas 14, 18
Tortugas Formation ................. 22, 28, 29, 31-35, 38
toulae; AMUSIUT 2 3.6 s3 5 'e ete one es 18 ere eB 72, 81, 84, 84
tOUlAl, SGNGUINOlATIG <i cc seri cde ora ae he ayant ws Ge Howie. whee 38
MPTES VATSENES? ays sc aceite sue Olekope Reema rohan 38, 77, 80, 81
Triceratium inconspicuum var. trilobata Partial Range Zone .. 39
Trinidad Formation ..: ..2.5.602e026++4 56, 99, 100, 102, 103
Crimitaria: DEpOrimetts: <8 a6 6 oso ees hot Sees hereon aA > 49
Trophon:sp.,Ch. Forreria belchert « so ciea iia cae 5 BS eS 31
tuff of El Canelo, Puertecitos embayment ............ 20-71
tuff of Mesa el Tabano, Puertecitos embayment .......... 70
Tutt of Sam’ Felipe! i .2 rece: 3.5 so nianges Sia ancnan ad amma ae 69-71
tuff of Valle Curbina, Puertecitos embayment ......... 20),74
tumida flexuosa, Globorotalid .cv.0 02 cca ets ewe we ae 104
Turritella ...... 22, 23, 31, 35, 36, 38, 42, 56, 66, 76, 100, 103

abrupta fredeat.: lo. 2 Po eo eee Go Els Sias.eoate 56, 100

ANGOTSONV. « Bg Bod ee hdreuere nce Barmah enanate Gp sa mementessiewaee 36, 38

DifAStI@ATA: srecaae g eatea she stein n et ee seco aney Muey Sree Bee 42

OSGI os aod x aun ase kc ae as-acnie SR GEES AIS SPSL ee aiea ea Neratheneet 36

PAMMUNENSIS: TAYTOGES 2 == 5 sieyaraoe Sassen 2Aivaana coinae a Gnathare a 42

WH DEFIGUIS Onana ic suaecveus jvth S/aays apare Gin ave = chy eNotes 66, 76, 103

infragranulata pachecoensis ... 6.002020 ee ee 35

MiMmMetes COUMENSIS. <0. 28. ew aie aoseres Fae ee oe a Gee a ear 100,

OCOVGNG =. saci s cai wine ke ot eee oe eae wives A108 22,31

PENUINSUIATIS. ean gee esns tenevs Byes. ad Sate, ate epayerars ernie 23; 35
Turtle Bay, Vizcaino embayment .....0. 0.200% 20005 e0e25- 9
Una de Gato sandstone, Loreto embayment .............. 88
Wvigerina PereBrina x. ic sy Sag 6. Sescne mee svde te, Bode ete 59, 61, 69
uvigerinaformis, BULIMING 0.3 eens dows oe os ee 87
uvigerinaformis, Galliherin@ 2. 0% occ ewes eens oes ea 104
uvula uvula, Globigerinita <2. 2 o.6206 6 ace so ween eS ce, 100
BvulG, GIODIBETINUNG cis 5 sieve ea 2 ae Ruste Ge a ee sie pe ES ee 93
Valle: Formationisc =25.9 0%< 4 earte sie woe oe eee 28, 29, 32, 34
Valle Group. 4.6 5. 54'e 20d, ait Gre Sategzaers ee ere, esate 28, 29, 33-35
Vallecito: Mountain) sz 5 cra Jeitentyiretatch ooo cog pule al ey ete ane 65
vanderhoofi, Anadara .......- 000040 e wees 51, -5257915,:93
yvanvileckt; AmuSSIOpeCteMn a. 5.0.3.6. 5. soy ecg: oa savas Saves 3 a Gre 35
VarpasihOrmatlon! .zniidteusvans attain soe, ose eagle eee e iesane 33, 34
Vasurm haitense i ia 26.4 b oo we id Gos masts Saree aries 56
VEQICHIL “OSUTEG s feca tious, dita, coe ade sees: © dave vigdeyia adnate 31
Venericardia sp: cf. V. nelsoni oc een oc oe eee ene 35
Venericardia VenturaenstS «sis woe idee nen Bie Cale 35
venturaensis, Venericardia ......... 0505 e eee eens 35
vertebrate fossils! sence a ves 19, 21, 26, 47, 55, 56, 64, 101
VESPETTNG; sOSTRED eo css fo eS eee ed doce SoH ENE pis 68, 104
VEIUS: FAY POLGBUS ees 2 ase se ere crane Bi ae athe Sia OE meee ale 101

146 BULLETIN 371

Vizcaino embayment ....... 10, 25-35, 38; Table 4, p. 32-34
Vizcaino: Peninsula s 2.05 ee hae ta ne ce as 9, 18, 24
vogdest, Oppenheimopecien. «20.6 ica one Ge ee ee 104
WesterniembayMment 22266: 2 22% So oe eee 10, 36, 39, 41
Western Magdalena embayment .............. Table 5, p. 45

Whitewater River, Salton Trough, California ... 9, 57, 60—65, 76
Wind Caves member, Salton Trough ..............-. 65, 166

WHULLCHI,. DRGIS: is gai ote ea eee ek eae Gog tere Gc ey we ae WL ey 36
WELCH FOVTEPIDY 5.252) bocce card ete.cl atop erehan ee eywtar AATTONAS: armel 31
LANUST, MUERG oie a -% we a oo Repel R Os Guts 400 whe be Bow eae 18
“Yellow beds,’ Purisima-Iray and western basins ..... . 42,51
Visidtofonmation® 28 <fcccccee saedes fee sue a anees ate ince 42, 101
Yuha' Buttes; Salton Trough) <3 5.405 6 oe iste Sw oie Seals sole eras 58
ZOTa FPOPMAGON v5.54 5.5 cents. deg ct as. at etree, @ dual austen ae Gels pay aes 36

Bulletins of

American Paleontology
Number 371 2007

(SEU ML

tes 1-2 of:

GRATIGRAPHY AND CORRELATION FOR THE
ENCIENT GULF OF CALIFORNIA AND BAJA
CALIFORNIA PENINSULA, MEXICO

By Ana Luisa Carrefio and Judith Terry Smith

La Mision
Basin

4
Ensenada,
Punta
China

1 “|2

San Diego Tijuana

Basin

El Rosario,
Mesa La
Sepultura

[Terrace deposi]

‘alluvium,

Isla
Cedros

Tanglomerales.

Punta
Eugenia

maring,

Bahia
Tortugas

Terraces

Plate 1. The western Baja California peninsula, San Diego, California to Todos Santos, Baja California Sur

San Roque,
Bahia
Asuncién

a stultorum

14 16

Purisima
Iray

15
Arroyo
San
Raymundo

7 arroyo

La Salada,

Santa Rita,
EI Rifle

Hipolito,
Punta
Abreojos

coquing of Onilieb.

San

Arroyo
Ignacio

Patrocinio

Rancho
El Aguajito
de Castro

vi Todos
Santos,
Arroyo

La Muela

San Quintin
volcanic field

ef | [at

bi
of Nova
‘and others

(1991)

mare strata

of Novacek

‘and others
(1991)

Olay
Formation

OLIGOCENE

Conglomerate}

Mission
Valley
Formation

Explanation

Radiometric age discussed in the text
Fossil age discussed in text
Unconformity or disconformity

Unit contact, unspecified

> Contact uncertain

Buenos Aires
Formation

Stadium
[Conglomerate

T Poway Group

Senipps
Formation

La Jolla Group

Dolicios
Fomation

4
Crewe
‘Mount Soledad

omas Las Tolas
Formation Lomas Las Tota:

de Cabra
Formation

Formation
‘6 Point Loma
| Formation —

Ee Marla
ee limestone
orAbbon
Botner
(3995)
atoucont
Sepuliura
Scale
ed Ss Cabrillo

Formation Rosario

Formation

Rosario Formation
Formation

UP;

Lusardi
to
Informal units of Kilmer (1963)

San Telmo \

_——

Alisitoy
Formation

Alisitos
Formation

CRETACEOUS

Paninsular
Range
Batnolith

Mesozoic

granite and

metamorphic
rocks

Peninsular
Range
Batholith

Peninsular
Ronge
Batholith

Peninsular
Range
Batholith

Peninsular
R
Batholith

Santiago
Pook
voleanic
tocks

rT
Batholith

pre-botholithic
basement
rocks

JURASSIC

TRAISSIC

Lower Rosarito
Formation Includes
Maasiventian strata

diatomite of
NcGove (1987)

Tortugas
Formation

Eugenia Formation
Colaradito Formation
Gran Canon Fin

Codros
opriolite Fault

contact

Metamorphic
rocks, including
Jurassic
Crotaceous
biuescnist
rocks

Vaile Group

Vaile
Formation
undivided

Los
Chapunes
formation

Porforada
formation
Fault

Eugenia
Formation

Valle
Formation

Chapunes

formation

Valle Group

formation

Eugenia
Formation

‘ophioiitic
rocks.
volcanictastic
turbidilos
biueschist:
bearing
Puerto Nuevo
melange
complex

undivided

Valle
Formation
undivided

|
|
|

Vaile Group

Asuncion
Formation

Pes Formation
arel [aR

>
at eval
El Yesa |

nr Salada Formation
*

marine and non-
———t___F marine rocks
basalt at Mesa

pis Galinas

Comer

Wsidro.
rt —

| Atajo Formation] ,

Comondd
Formation

San Ignacio

Formation tuffs.unnamed
volcanic and
volcaniclastic

rocks

tufts. unnamed

voleanic and

volcaniciastic
rocks

unnamed
sandstone

Isidro
Formation

San Juan Tutt

San Joaquin

Formation

Cerro

Colorado
Zorre, Mombor
Formation
Tol ise
ta Clara.
Formation“ Zacarias| |
Formation’

|siatorne|

=I)

San Gregorio
Formation

tuft ‘San Hiro

EI Glen Formation

San Gregorio
Formation

potters)

Cerro Tierra
Blonce Member|

mee

diatomnite
of McLean
Bothars

1987)

Boteqve
Formation

Balequo
Formation

Bateque
Formation

eae

Tepotate
Formation

Balionas
Formation ee ee

Baleque
Formation

crose-bedded
member

Santo
Domingo
Formation

For mation

bedded

member ‘ites

bedded
| member

Tepotate

‘cannonball

cannonball
member a

member

dui
conglomerate

La Paz
crystalline
complex and
Mesozoic
plutons. of
Aranda-Gand
Paroz-V. (1989)

Valle
Formation
undivided

Valle Group

Fautt|

BS115my

No basement ment

rocks exposed

No basement No ba

fochs exposed

No basement No basement

rocks axponed

No basement
rocks exposed

racks #xposed

Sierra de
San Andrés.
Cedrox complex

Fault
contact!

sandstone
mombar

breccia
limestone
member
Puerto|
Escondido|
uf
tadiolariart

San Hipolito Formation

Salton Trough, California to Islas Tres Marias, southern Gulf of California

28 30 31 Islas 33 Boleo Basin} 35 36 Loreto embayment | 39 40

Puertecitos la Se | re
Bahlas de isla Angel NE margin | San Lorenzo Isla Isla 34 Bahia Bahlade [37 San Carlos, Sanduan 43 44 Tres Marias

embayment i
Guadalupe and de la of Sierra and Tibur Sant i Isl San Telmo F
; ‘on San Esteban anta Concepcion San Nicolas sla ulet de |; EI Ref 7 Isla
de los Angeles Guarda Las Animas | Las Animas Rowalla dal\Garmen 1 Tambablehe?| c@ a Costa alalaeay eaeeneh Marla Madre
CuO Sank beach Sea Sepeal mos E DUTT aaa
+ —
ies tulls and (miarine rocks
1 aleia | conglomerate
7

Aes
coauin pe es
ae

marine
sediments one
marine sedimentary SiPrea Pareain arava f
mo 25 Cinta Coloraae
‘ores af Er Coyote

septentrional, pyrociantic [AT aa Me marine Holt ot al (1997) _ | Conglomerate
roeks s ES

andenitic lavas Oasonie (1982) |

‘and tuils

__MeGoy (1984)

basal coquina

— |»

ST Pn

volcanic breccin, un vsal
sanduione facies

Sequence 2

a” Gace dome 12 Ma

se Breccie | =| rolcanic and
TA) dashile i voleaniclastic
sandenibe-dacitic lavas and) t-———— angositie breccia
fossinch sediments of Sowlan (1991) 3 " unnamed marine
11200. a a porphyritic nonman
Ricasén eed tacie volcaniclaatic rocks

Formation

>
= Units of Aranda-G- & Parezv. (1!

arose Andosite of
sandstone ‘chs of 8.6205 Ma . Sie 1a Lucia of
‘af Stock of af ‘of Nagy (1696) Ledeama-VAzquaz (2000)}
(1996)

192% Ma
Gastil of al (1999)
Ei Clen Formation

Anactare varcnctocd -24 Me
‘aerns and penne tant. *|

Minitos cogoreee S Dn Thee
Formation Salto Formation of

andesiion

chert, carbonate rock
channelled red arkose.

ond pet 1
bbe bec Polongs | Ledesma-Vazquez (2000)

Formation

Unite of McFall (1968)

Salto
Formation

Eocene (7)
quartzone
rec-bedoea
sandstone of
MeLoan (1988)

Explanation
Radiometric age discussed in the text
. Fossil age discussed in text
—— Unconformity or disconformity
_ Unit contact, unspecified
| > > Contact uncertain

granitic
grannic patnolinie
petals Baise Bn iriees metamorphic paaecene “ basement nestor! ond
Menon ‘and granite a rocks ie and prebaiholithic
arene 9 . 4) tholith granitic and granitic ana r granite and
Fectosetee Hangs font rocks molamorphie metamarphic augments granodiorite

basement rocks renseted Paleozoic a reunoue
basement rocks basement rocks basement

LaPemine
neo

. ) McFall (1968) 7 bat a Bam Mus

“ua

routs

Gastil or af (1979)
McLean (1988)

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